Part of me really wanted to say Jupiter, but I just really like its moons. Europa, Callisto, Ganymede. They are all pretty cool. Jupiter itself is a pretty cool planet, I just like its moons better.

Uranus is pretty spectacular. That one may be my favorite actually. Speaking of moons, its moons are named after different characters from classic literature (mainly Shakespeare I think? Oberon and Titania are the only names I can think of off the top of my head). That's pretty neat!

You can't go wrong with any of the planets though.