I own a 190E-16 and a '89 420SEL. Both seem to reality good cars. The 420sel has 38K on the clock and maintenance has been relatively inexpensive. I've heard alot about tranny problems when the car gets up in the mileage (around 80K). The 190 has seen more maintenance in the 6months since I've owned than I would care for. Its however quite special and I intend to hold it and drive it for awhile. It only has 32K on the clock.
Since you've done most of the maintenance by yourself, what type of manual did you use as your guide? I think of myself as fairly handy, and I would like to maintain myself.
Anyway, my personal choice would be the 420sel. Smooth, powerful, fairly luxurious and built like a tank. If its for your wife, go with a tank.