I don't think one is inherently better than the other, but they will play very differently (and you should take into consideration what kinds of abilities you want to design).
Even when I played games with an ATB gauge, I usually changed the settings to "wait," which would pause the ATB system - and thus the enemies, as well - while I looked through my menu of abilities, because I didn't want to be penalized for having to scroll to Fire 3 or something.
To Oscar's point, ATB will probably make your battles feel a little more frantic and faster, because you're forcing the player to make quick decisions or be punished for thinking too long. How much they're punished is up to your battle design, but I think you have to cut the player more slack on enemy abilities with an ATB than a CTB.
CTB has more license to punish players not for making slow decisions, but for making bad decisions. You can arguably make more complex battles with CTB because you can allow the player lots of time to consider their response. The flipside to that is that a CTB almost requires more complex enemy behavior to make up for it.
However, if you want to gear more for players who enjoy "twitch" reflex play, ATB is definitely the better way to go - and it's also hard to create a sense of urgency with a CTB system.