Hi:
I had a 3320 (now a 3720) and looked at the 3203's but didn't consider them due to lack of a Mid PTO.
I think the HP on the 3203 is the same as the 3320 (1/2hp diff), not the 3120 so From a HP perspective both machines (3320/3203) are similar.
You won't get ANY of the electronics on the 3203 (no load match, no cruise, etc.)
You CANNOT get a Mid PTO on the 3203. No MMM, no Snow blower, etc.
It has only a 2 range tranny vs a 3 range tranny on the 3320.
It has a mechanical vs e-hydro. (In all honesty, I prefer the feel of the mechanical hydro (like on my 2305) but you don't get any of the electronic features but I would miss the 3 range tranny.
The 3203 only takes the 300 loader (not the 300X or 300CX) The 300X and 300CX lift quite a bit more than the 300. (Was a biggie for me).
You cannot get a third SCV, Power Beyond (I think), divert valves, etc. on the 3203. Although
I'm sure a dealer could put things like power beyond on it.
And as mentioned, the seat isn't as comfortable, etc.
I also think the Tires available on the 3320 are bigger than those available
on the 3203 but I'm not sure about this.
There probably are a few things I forgot to mention.