This may sound odd, but I always felt the Stern Electronics popbumpers had a special 'feel' to them, which I like very much. They feel great and the action is not as meh as they are these days.
I also prefer popbumpers that aren't locked in, so they can add randomness to the game. Some may feel it's not fair if a popbumper is able to send the ball straight into an outlane, but I think it's a great equalizer, adding a bit more luck-factor to the game.