Sphax PureDBcraft! The main bonus to it is that it has a dedicated texture-modding community where people will offer textures they've made for a whole rainbow of Minecraft mods... though many are still WIPs, so my texturepack isn't complete. If I could stand Vanilla for more than five minutes, I'd probably just stick with that, because having different resolutions and styles is kind of jarring. But when I play vanilla, my favourite is a 16x16 texturepack called Jolicraft: Though there's a lot of other good ones, too. A while ago I actually put together a list of nice (updated, Vanilla) texturepacks. It's here if you want to look them over, though it's definitely not comprehensive, or anything.
