Both have their advantages. KDE is the best for people who love eye-candy, because it has features like window transparency, shadows, animated things, etc. But because of all these extra features, it is very bloated, and is quite slow. Gnome, on the other hand, is more lightweight. It still has quite a lot of eye candy, but I find it quicker, easier and simpler.

Of course, the best way for you to find out is to try them yourself, and find your favourite.