If you only have time to watch one movie, watch Treasure Planet.
If, on the other hand, you have time to watch two movies, I recommend watching Treasure Planet twice.
Actually, if you just want a good movie in general? Treasure Planet's pretty damn good.
Atlantis, on the other hand, goes to amazing lengths to avoid both character development and suspense. Seriously, it's actually impressive. You might want to give that one a pass, unless, like me, you want to marvel at ways to fail at writing good plot.
Treasure Planet's good though. Go watch that one.