Tron is it for me. I love good coasters. I picked it over GOTG, because I'm still annoyed that's going into Epcot, I prefer outdoor coasters, and I don't know much about how it will be as a coaster. Tron is a more known entity for me.
Not really all that excited for Star Wars. We're planning on taking a friend in 2020 to see it, but I'm not into simulator rides and that's about all I've heard about so far.
At first glace it seems like I would enjoy Tron more but again, I am annoyed at how short of a roller coaster Tron will be as Guardians of the Galaxy is supposedly going to be one of the longest indoor roller coasters. So long as the coaster tops 2 minutes of ride time, I feel like I could potentially enjoy Guardians of the Galaxy more although I will always be skeptical of its inclusion in EPCOT.