Honestly, I like Crono a lot better. Serge looks almost like he's wearing a bonnet half the time, and the twin-blade weapon is kind of stupid. Mostly though, I just don't like his name. Besides, what's with the outfit?
So what if Crono's concept art looks like something out of DBZ? There's barely any concept art to begin with, and the sprites in the game are very well done. Because of that, Crono's character comes across as a lot more animated and lively than Serge's.
Really though, I always felt the Chrono games were slightly lacking when it came to character design. If there were ever another game, I'd really like to see someone like Hyung-tae Kim, Tite Kubo, or even just Tetsuya Nomura do the concept art.