Both of them are non-stop action sequences that keep building and building and should be a masterclass for filmmakers on how to construct cliffhanger action scenes. I love them both for different reasons. The final action sequence in AOTC (which I count as beginning when Padme and Anakin are wheeled out into the arena) is just an insane series of events that goes from a Ray Harryhausen style monster bash to Jedi warfare to Clones vs Droids to a lightsaber duel that is topped off with Yoda whipping it out in perhaps the most crowdpleasing scene of the whole saga. What I love about ROTS is that it feels like the end of another movie, especially with a lightsaber duel that we'd never seen at the beginning of a Star Wars movie before. The opening shot finally matches the opening of ANH, and the fact that we get to see Obi-Wan and Anakin as friends and Anakin as a great pilot addresses two of the chief complaints about the other prequels. Both of them are marred (in some people's opinion) by 3PO's slapstick in AOTC and R2's in ROTS, though I didn't have a big problem with those attempts to inject humour (they worked better than the Jar Jar slapstick in TPM). I still think the AOTC battle is slightly more fun, since it has more build-up and includes every character, but I can watch both of these sequences anytime and never get bored.