The Tandy 1000TX was released in 1987. Its successor, the Tandy 1000TL was released in 1988. The TL was mainly a refresh of the earlier machine, with some enhancements. However, in its efforts to become more PC compatible, some things were lost. Let's compare each machine.

Consider what both machines possessed in common :

80286 CPU @ 8MHz in PLCC Socket

5 ISA Slots

TX - Composite Video Output

TL - 640x200x16c and MDA/Hercules Graphics Emulation

Composite video is useful to recordvideo from the computer, since there are many, many devices that willrecord a composite video signal, even a not-quite standard signalthat the Tandy outputs. It is also works very well with games that use a true (Maniac Mansion, Starflight) or effective (King's Quest) 160x200x16c graphics mode. In this mode, there is minimal artifacting and the colors presented are generally close to their RGB counterparts. True composite artifact color games, generally made for the IBM CGA card, will show incorrect colors which no amount of fiddling with the tint control will perfectly fix. Still, the results will look much better than on an RGB monitor. However, recordings using the 320x200x16c mode will not look great, because the composite video signal does not have the bandwidth to keep up with the color changes. The TX can also support a true 200-line 80 column text mode. The TL will display a rolling screen using the MODE 200 command that came with the system disks. You can use an updated MODE.COM from the RL system disks.

The Tandy 640x200x16c mode was rarely used in games, and those games also supported the corresponding EGA mode and all of the known games support VGA as well. Deskmate 3's draw application uses it, but Deskmate 3 does have VGA and probably EGA drivers. The built-in graphics controller can also emulate MDA/Hercules, but there are three issues with it. First, if you use the machine as an MDA/Hercules card, you will also need a TTL monochrome monitor like the IBM 5151. Second, since there is only one video output port, using MDA/Hercules disables the built-in Tandy graphics support, as you cannot see it anyway with the MDA monitor connected to the port. Third, some games will detect a Tandy 1000 and insist on using the Tandy or CGA graphics modes. It can be useful if you have upgraded to VGA, but then you could simply obtain a generic system for a VGA/MDA combo.
The TX can add a MDA or Hercules card and retain the ability to output Tandy graphics to a separate video monitor. Still, some games will autodetect Tandy and not work correctly with the Hercules card.
While both the TX and TL support upgrading to an EGA or 8-bit compatible VGA card, there is a very nice utility called VSWITCH that will allow you to switch between the built-in Tandy video and VGA. More recently, someone made a similar program called ESWITCH for EGA cards. However, due to the differences in disabling the built-in video on the TX and the TL, the program only works in the TL or later Tandy 1000s with 768KB of RAM.

Advantage - Tie

Audio :

TX - 3 Voice Sound & Sound Blaster 1.0-2.0 Support

While the TX only has the basic 3 voice chip, it also can work with a Sound Blaster 1.0-2.0, or any other 8-bit sound card that only works with DMA1. Many early Sound Blaster-supporting titles only work if the card is at IRQ7 and DMA1. However, because the built-in joystick port cannot be disabled in software, the gameport of the Sound Blaster must be disabled.

The TL has a very decent mono DAC built in, which can use the internal speaker for output. The ADC can sample at a higher rate than a Sound Blaster 2.0, but in the TL it is speed sensitive. While this is immaterial to Tandy Deskmate, third-party programs may have difficulty with recording. Some early games like SimCity and Outrun only support the Tandy DAC and not Sound Blaster. Overall, many more games support a Sound Blaster than the Tandy DAC.
The DAC was never released as an add-on card, so at its original ports (where many games expect it) it is unique to the 1000 TL and SL and successors up to and including the RLX. The TL's joystick port can be disabled in software, but using a Sound Blaster 1.0 or 2.0 will cause the system to freeze if the Tandy DAC is used. Using a Sound Blaster Pro, with the DMA channel set to 3 and the IRQ set to 5, would allow the Sound Blaster and Tandy DAC to work fine. Many early games refuse to work with a Sound Blaster unless the DMA is set to 1. Additionally, the DAC and the built-in joystick ports cannot be used at the same time, so a game supporting the DAC is not likely to read the joystick port, built-in or on an expansion card, while using the DAC.

Advantage - TX

Drive Bays :

TL - 1 x 5.25” slot & 2 x 3.5” slots

Two 5.25' slots allows for more flexibility than one 5.25' and two 3.5' slots. If you wanted to install a 5.25 floppy drive and internal CD-ROM, you could do so in a TX but not a TL. However, the TL offers a more appropriate setup of one bay for a 3.5' floppy drive, one for a 5.25' floppy drive and one for a 3.5' hard drive. With a TX, you would need to use a hardcard. The 3.5' bays on the TL are not generally useful for external drives because the faceplate is moulded into a certain shape and cutout. The faceplate is made of plastic, so it can be dremeled out.

Advantage - TL

Keyboard Support :

TX - Tandy 1000 90-Key Keyboard or Northgate Omnikey 101-Key Keyboard (with adapter)

TL - Tandy Enhanced 101-Key Keyboard or Tandy 1000 90-Key Keyboard (with adapter)

The Tandy 1000 Keyboard has 90 keys and is slightly awkward to use from a modern perspective. The keys use springs, but feel mushy. The interface is proprietary to the 1000TX and earlier 1000 machines and the Tandy 2000.
The Tandy Enhanced keyboard has the standard 101-key layout, but feels too stiff. The keyboard can automatically switch into XT or AT mode, and can work an IBM PC Model 5150 or a 2014 motherboard with a PS/2 port.
The TX can use a Northgate Omnikey keyboard with a special passive adapter cable for 101-key support. You will not be able to use the F1-F4 function keys when booting with the Northgate.
The TL can use a 1000 Keyboard, with a special passive adapter cable. The TL can use any keyboard that supports XT operation, including the IBM PC Model F keyboard and the IBM Model M keyboards made prior to 1993. However, there are some games that expect a 1000 keyboard and will refuse to work at all (Snow Strike) or freeze (King's Quest Tandy booter) if the wrong key is pressed with a standard XT keyboard.

Advantage - Tie

Real Time Clock :

Built-in RTC

The TL has a standard RTC and uses a replaceable CR2032 coin battery. The TX requires a no-slot clock like the Dallas 1216E, which has a built-in battery and is seated under a ROM socket. The height added by the clock chip can make the slot next to it suitable for only short cards. Tandy DOS 3.3 has built-in support for the TL's clock, the TX requires an upgrade.

Advantage - TL

Heavy Shielding inside Case

The TX has shielding virtually all around the motherboard, making the internal slots and jumpers difficult to get to. It's case cover is plastic. The TL apparently solved any RFI problems of the older machine by using a metal case cover, because there is no shielding getting in the way.

Advantage - TL

Configuration and Built-in Software :

DOS & Deskmate in ROM, EEPROMSettings

The TX is configured by eight jumpers or dipswitches. The TL has five functional jumpers/dipswitches, the rest is configured by a program included on the DOS disks. The TX uses Function Keys, pressed on startup, to use the monochrome mode, swap floppy drives, use the 40-column/200 line TV mode and set the processor to low speed.
The TL does all but the TV mode via the setup program. The settings are written to an EEPROM. If that EEPROM fails...

The TL also has a portion of DOS and Deskmate 3 in ROM. This is only useful if you do not have a hard drive. If you have a hard drive, then the DOS on that will boot and a standalone version of Deskmate may be required to be installed.
Advantage - Tie

Bundled Software :

TL - Deskmate 3.2 & DOS 3.3

DOS 3.3 is better than DOS 3.2, there is no doubt about it. Since neither the TX nor TL can support a high density floppy drive with its built-in controller, the best quality DOS 3.3 brings is its support for more than one 32MB hard drive partition. However, the TX can use Tandy DOS 3.3 without any difficulty. Deskmate 3 looks similar to Personal Deskmate 2, but 3rd party programs can easily be installed to it. Of course, you can upgrade the TX to Deskmate 3. On the TL, Deskmate 3 has music and sound programs in the ROM. The music programs in Personal Deskmate 2 and Deskmate 3 should share compatible files. However, the DOS installable version of Deskmate 3 does not come with the music program, so you will need to keep Personal Deskmate 2 for that on the TX.
Memory Upgrade :
The TX and TL both allow their memory to be upgraded from 640KB to 768KB, and when upgraded the video no longer encroaches on the conventional memory. DOS will report 640KB available. Both are upgraded in the same way, by adding four 64Kx4 DRAM chips. The TL automatically will detect the chips, the TX requires a jumper to be removed. However, the upgrade is incompatible with certain programs (detailed in a later post), forcing you to use CGA modes for those games. To disable the upgrade, you must physically remove the chips in the TL, but you only need replace the jumper in the TX.
Advantage - TX