I like fire, not necessarily because it's strong or cool, but because more of my favorites are fire-type than any other. Dark, flying, and water are close seconds, though. Water attacks are very strong and come in handy often, and Gyarados is arguably my favorite since I haven't played a Pokemon game without having one on my team, but I'll have to say fire for this since I'm not really all that fond of any other water-types but Gyarados. I guess for me it isn't so much the type itself as it is the Pokemon of said type.