My general rule of thumb is to go with the car that has the most service history; you'll obviously have fewer unknowns. However, the 96 850's AC issue could potentially be very costly. Most everyone here will tell you that the evaporators fail commonly on these models, and when they do, you have the tear the car apart to get to it, very very costly to have someone do. I'd be absolutely certain of the AC problem before price negotiating for the car.

Another absolutely necessary thing on these cars is the timing belt, make certain it's been replaced at the required interval (94-97 850 at 70K miles, V70 at 105K miles I think). If the belt brakes, the engine is an interference design and will destroy itself.

ABS modules do fail, but I think more so on the 850's (someone correct me if I'm wrong). I think it's hard to tell if you don't have the ABS light already on, but fixes for that aren't too bad, and there's someone on this board that actually repairs them for people at a good price. I wouldn't regard that issue as a show stopper.

All the FWD Volvos chew through bushing components pretty quickly on account of all the front end weight, so listening for clunking while driving an unknown car is a good idea. Checking for things in the service records like CV joints and control arm bushing replacements is also good. At 216 Kms, some of that stuff was probably replaced on the 850 if they took care of the car.

I'm a red block to white block convert like you may soon be, and I really like these cars, don't be afraid of them. Their ride comfort and luxury outweigh the increased complexity. Just make sure you get one with service records, or exercise extreme caution on the unknowns, especially the AWD unknowns, as mentioned in the other posts.

Cheers.