Single channel JCM 800s were the 2204 (50 watt) and 2203 (100 watt). There also were combos (4010 = 2204 in a 1x12; 4210 = 2204 in a 2x12). They're essentially the same as the JMP 2204 and 2203 models, but by the JCM time period, there were no more mustard caps, etc., so maybe the JCM tone is a bit more aggressive. No frills (one channel, no loop, no direct out). Originally vertical inputs, they changed to horizontal in maybe '85? It was cost-cutting (horizontal inputs allowed all the pots and jacks to be placed on the PCB. For the 2204, the only change to the actual circuit (I think) was an increase in the plate voltage. For the 2203, there was even more cost cutting: the change also was accompanied by reduced power filtering, which does impact how they sound and feel. US models have rocker switches and use 6550 tubes. UK and Canadian models use toggle switches and EL34s. My JCM 800 has the 6550 and sounds like what you'd expect a Marshall to sound like, so I think any focus on the type of tube is overblown.
There also are two channel JCM 800s: 2205 (50 watt) and 2210 (100 watt). There were combos too, but I can't remember the model numbers off the top of my head. These have two channels, an effects loop, and line out. Earlier examples may suffer from "channel bleed." I think that was sorted in around 1987. At least for the later models, more gain available than the 2203/4 amps. I don't remember what tubes these came with, but I'm guessing it was the same as the 2203/4 amps.
The 2203 seems to be the most desirable, though I (and others) prefer the 2204 because it's warmer. The 2203 has more low end and high end, but the 2204 certainly isn't lacking either. Late '80s 2205 and 2210s are great amps that are still somewhat under the radar. The early '80s 2205 and 2210 aren't all that great. The horizontal input 2204 amps are OK, but I'd avoid any of the horizontal input models because the price difference between them and the vertical input models isn't big enough for me to want to deal with circuit-mounted pots, lower power filtering on the 2203, etc.