I have a 1995 Fleetwood Brougham and can't think of too many differences, but I love the car overall. The side-view mirrors are smaller on 1994 and they aren't as nice to use, but they also don't have the Dumbo-ear effect, either. What I mean by that is, like with most new cars, when you are behind the car you can see the mirrors sticking off like big ears on a face and they are more easily hit and knocked-off by other cars. The bigger 95 and 96 mirrors are better for visibility, but I must say I like the mirrors on those older Fleetwoods where they don't stick out beyond the body. The 95 and 96 mirrors do fold toward the back of the car, so if you bump a car they will collapse, but if a car going forward hits you parked, they won't. If I park on a narrow street I will fold them in to be safe since, if hit, they will not collapse forward. My older Fleetwoods don't have that issue.
There is the OBD I and II difference. Being OBDI and pre-1996 gets you out of some tests and regulations depending on where you live. Not only is there the OBD I and II thing, but some of the other devices on the 1996 are unique, like the radio/tape/CD player. The only thing I usually don't keep stock on my cars are the radios, but all of the mid-90's Fleetwoods have there own unique harness and set up not shared with other cars (not even other Cadillacs) which makes it harder to put in aftermarket stereo equipment. I really wanted a CD player in my 95 when I got it, but it didn't have one. I could find no one who had wire harness adapters for the car. I was then just going to hard-wire in an aftermarket control head, but adapters for the device to fit nicely into the instrument panel were also not to be found. I have a 76 Fleetwood that I hard-wired and modified myself to fit everything handsomely, but I decided the best thing for the 95 was to get a Cadillac CD player (which was obviously not an option on the 76). Doing all of this made me notice at a future time that the radio in the 1996 (and I think the climate control) were different, and thus must be unique to that one model and year since they were discontinued after that. This would make these items even harder to find if they needed replacement than their 93-95 counterparts.
95 and 96 have a button to disable the traction control and I believe 94 doesn't, which is bad if you need to spin the wheels. I have rarely used it, but twice in the last decade I have and would have been screwed without the ability to disable it. 95 and 96 also have a quieter cam set up that is supposed to make the engine run quieter. I've never listened to the engine of a 94 vs. a 95, but in theory the cam should run more quietly according to GM. 95 also got a more durable torque converter clutch over 94.
As far as ride goes, my 95 is the best riding car I have ever driven in my life, and I've driven a lot of cars. I do not have the towing package, nor would I want it if it meant making my ride less smooth and soft. My 95 has the FE1 soft ride, and it is so great because it is so soft, but isn't overly boaty. It holds steady on the road, yet eats up the bumps. If you're into that nice ride (if not, why have a big RWD Cadillac?), I'd avoid the towing package with stiffer suspension. The LT1 has more than enough power and torque as it is, so why eat up more gas on the highway and give away that smooth ride just to get a tiny bit more off the line?
All-in-all, I'd go 95 with no tow package (unless you need it), but not just because that is what I have. I just happen to get a 95 since I would have taken any 94-96 back when I was looking, but in retrospect with what I know now, I'm glad that's the one happened to get.