I've maintained my daughter's W115 for the last 6 years and it has been very reliable. The 115 is more primitive than the 123, which can be good and bad. Personally, I would just look for the best car and not get hung up on the version.

One thing to try to assess on older cars is the condition of the suspension, including the ball joints. Front suspension is expensive to have replaced ($1K ballpark - not including new springs) and no fun to do yourself. The rear suspension isn't too bad.

Scotty