I've often thought about this, but I could never really decide what category I fell into.
I usually start off by thinking I'm a Johnny. I'm an engineer by day, so I love to understand how everything works; I like to explore all the subtle interactions between cards and come up with devastating combos that others would probably overlook. When evaluating new cards, my first thoughts is, "How can I break this?", not so much in the sense of winning, but more to just use the card for unintended purposes.
I also enjoy tinkering with my decks, tweaking them until they're really good and can win very consistently, which I guess gives me a Spike streak.
Lately, I've been playing a lot more (during lunch with some friends at work), and I've gotten more into the social aspect of the game. I try not to play my really powerful decks very often, often retiring them after I've tweaked them to the point where no one wants to play against them anymore, which I suppose is a Timmy thing to do.
So, I guess my answer is that I'm a little of all 3 types...but I still fancy myself a Johnny.