Reliability? Well, I think the comment stands. I wouldn't want to be paying for a lesson or to hire an aircraft that is a bucket and quite likely to go U/S when I taxi out.
Learning how to deal with problems (whilst in training) should not be because you get the actual problems themselves on a frequent basis. For example the first time I learnt how to deal with a screwed vac pump and loss of instruments was not because it suddenly happened to me, but rather from good teaching and preparation. Then when I had one bust whilst hourbuilding it was a non-event.
Remember by the same token, old doesn't mean unreliable or unsafe. They still need to pass the same 100hourly. So long as they're maintained, there isn't a problem.
As for MB Vs other, I agree the only reason I'd stay away is for cost again. I cant justify the landing fees or wait time on the ground.