Definitely play them before you make a decision. A game can look and sound the bees knees but you won't know until you stand in front of it and experience it for yourself.
Personally, I love Tron and it's my favourite Stern. It ticks all of the right boxes for me including sound, art, play, challenge and theme. The one point worth mentioning though is the challenge. It's fast, hard and not friendly. If you get frustrated easily then it may not agree with you.
I've never liked XMen in any regard. I guess the theme is ok but everything else just doesn't work with me. The sound (besides the main background music) is kind of bad, especially the call outs. The wolverine toy looks cheap and silly. The play field is way too busy with (what I perceive anyway) a million things going on. There's just one thing I like about it and that's the multi ball start sequence where they all collect in the middle of the play field, spin around and then all fly off. That's possibly the coolest magnet trick in pinball for me.
Tron all day every day.