If you have a preference for fast flowing games then I would say without a question go for Tron but if you want to add some variety to your line up with a "stop and go" type game then TSPP would be a good choice.
I've owned TSPP twice, the first time around I was only 2 months into the hobby and gravitated more towards game where you were rewarded easily with satisfying shots. TSPP felt like a chore and didn't have the same flow as my DM or WCS94 at the time. I ended up doing a 2 for 1 trade for it and that is how I got my JM and I500 which I enjoyed playing a lot more. Fast forward almost 2 years later, I now have a difference perspective on playing and appreciate objectives and mode progression more so I thought I would give TSPP another try as I didn't really give it a fair shake last time. I did enjoy it more and got to see a lot more of the game but in the end it still felt like a chore to play and I only wanted to play it say once or twice a month.
Now Tron on the other hand I could play a few times a week and it doesn't feel like a chore at all if anything it always leaves me with that "one more game" type feeling. From the moment I hit the Start button, the music sucks me in and I have never even seen the original Tron before and only recently watched Tron Legacy. Now all the call outs and modes make sense to me and I've had Eli's developer's kit in the game since March/April and that really added to the game play experience too.