I have not played Iron Maiden but from videos and other input it could very well be top of the list. I own a MET pro and love it. Just a great, solid game that is flat out fun to play. With a colordmd, it holds up well with all the new games. While not my top pick, TWD does have a lot of fans. SW pro doesn't look like much but is a lot of fun to play. I would push GB off the list as far as it will go down. Fun for a short while but quickly gets old with terrible design flaws.

Bottom line, I would say get Iron Maiden new. It has the LCD display, unique layout, and 4 flippers and still relatively new. Find a good deal on a MET pro used once you save a little. They have been in production for years so tons of them out there. Prices have been pushed up so no reason to spend big money on one. Get some game time on other titles and see if they are worth getting.