Steel. I've got to say, many of my favorite pokemon are steel, and they can be a real challenge for an unprepared team. (Does Steven come to mind?)
I think I'd rather be a Gym leader because it's their job to protect the town and help rookies out, while the Elite Four just sit in a big room waiting for challengers. I generally find most gym leaders more memorable than elite four members. (bar Lance.)
If i had to choose a region, I'd probably go for Hoenn. There seems to be a prevalent number of steel types that make the region their home.
My team would probably consist of Aggron, Metagross, Scizor, Steelix, Skarmory and Magneton. I know there aren't alot to choose from but hey, that's all I've got.