BDK all the way-- (Disclaimer: I am a BDK owner). There is much more to do on BDK (many major and minor modes) and cool toys. Quality game (metal ramps, chain-driven crane etc). Tron has a 3rd flipper, which is really cool and neat ramps (cheap and prone to cracking). It's definitely more "in your face" than BDK, but it's Tron and the Tron theme is very lame. At least with Batman, you're getting the Chris Nolan version of the films as the theme and let's face it-- that's about as cool as you can get.
Don't get me wrong- Tron is fine fun, but it gets way, way overhyped on this board.