Good Grief. This one's hard.
I think I have two:
Fire: It burns everything in sight, super powerful, learns Ground type moves, whoops most Gyms, keeps you from freezing in the cold, and has a lot of my favorites in there.
Water: It whoops up on Fire, and it learns Ground type moves, 70/30 chance of whooping most Gyms, I love to swim in it, I'm part frog[well, actually, I just swim like one, but very, very fast], water is the most important thing we need in our bodies, it's blue or green, it's nice to have after a hot day, and has a lot of my favorites in there.
So, I think overall, I will choose the Water Type.