I think that Glen offers the most wise response. It totally depends on the level of knowledge and skill posessed by the owner. I know plenty of people for which there has never been ANY car built on which they could so much as change a flat tire.
On the other hand, I know people who can do darn near anything.
This is one of those questions that is sort of like asking "how long is a rope?" There's really no fixed answer until you do some measurement.
All that said, what comes to mind are the 114/115 and my favorite choice the 123. I have been able to do everything myself on my 124 car, but it isn't always pleasant. Simple things like removing door panels or kick panels from under the dash borders on being a pain on the 124, while these operations are as simple as falling off a log on the 123's.
In particular the four cylinder 114/115 and 123 cars are extremely accessible under the hood.
Have a great day,