Well, I've had a 190E 2.3 Liter with a 5spd and now have a 500E so I might be able to provide you with some insight on this.
The 190E is certainly a fun car to drive especially in 5spd form. It isn't very powerful but definitely holds its own. It is a very tossable and nimble car and sticks like glue with the right set of tires. I installed Koni shocks and struts all the way around as well as Eibach sway bars and springs. I also had 205 tires on 15 wheels. The car could take a 90 Degree turn at 35mph!
The 500E is quite a bit heavier and definitely feels heavier when you drive it. It does however handle extremely well and can be considered athletic.
I recently took mine into the mountains for some spirited driving, where there are multiple switchbacks and tight turns over a 30 mile span just to give you an idea. The car handled superbly and every other car had to use the turn offs (a widened area of a two lane road to allow faster cars to pass) to get out of my way. It's especially nice to have 325 horses pulling you up a steep winding hill! My speeds were much much faster than posted limits, don't want to incriminate myself though.
I think the biggest thing you'll notice about a 500E is that is totally effortless to drive extremely fast. The car doesn't require the attention of a 190E and doesn't have the driver involvement. It has descent road feel and is quite comfortable also. It is also much much more stable on the highway.
I'd recommend either car, just depends on your tastes. As far as maintenance I would imagine both cars would be equal. The 190 is much older, although simpler and will probably need some new hardware. The 500 is newer but much more complicated, but you can still do most of the minor repairs yourself.
Go out and test drive them, you'll know immediately which you prefer.