I started on the DMD's but now also gravitate to the SS games for the same reasons you mentioned. In particular the Early 80's Bally's and Gottlieb system one games really float my boat at the moment. I currently have two of the Ballys and one system one game coming later in the year but I can only see myself buying more of these sorts of games in the future. I think it's a combination of great art work, easy to understand rules and what can quite often be brutally fast (read short) games.
How many times do you play one of these games and felt like you almost cracked it? If only you could have kept the ball in and dropped that last target! It's what makes me hit that start button again. As exciting as a good game on a dmd can be, many times after I've finished a game I look at the machine and think that's enough for now.
 All that said, I think variety is the key and a few games from each era to suit your mood it the way to go.