Tough call, tough call. I grew up with both so I hold them close to my heart. I really enjoyed the TRON themed tunnel on the old People Mover back in the day, but I also really loved Return Of The Jedi as well.
I suppose it all comes down to the current theme of Tomorrow Land. If it stays similar, than I'd say Light Cycles, if it gets a complete Star Wars overhaul, Speeder Bikes.