2" Flipper era: go with an add a ball like Cowpoke.
3" flipper era: I'd go with one of the later Williams games. I love the artwork on Gottliebs, but the Williams games from the early 70s seem to be much faster compared to their Gottlieb counterparts. Really, though I can't go wrong with either company.

True, but there is more to an add a ball than just getting an extra ball. Most EM games set to extra ball only allow you to get 1 extra ball per play. Add a ball games allow you to get as many as 9 on a single ball, depending on how many bally you have left when you begin that given round. What I like about add a balls is that instead of just trying to max out a score, you have the added challenge of trying to get to the 10 on the bottom. Seeing the 6, 7, 8, 9, and 10 (I have mine set to 5 balls per play) is not easy to accomplish, but generally more doable than it is on traditional games that award free replays.