Jonathon,
First off welcome to the dark side! We can all tell you why you should join each ARTCC, but it only comes down to what you want. If I were you, I would go some place that interests you. A lot of people control in the ARTCC they live, but it is up to you. Personally, I chose Atlanta because I grew up in Atlanta and I wanted to work my "home airport". It had nothing to do with the fact it is the busiest airport in the world and 3rd in VATUSA, 8th on VATSIM. (Sorry, Had to throw some advertisement in:)
I would also recommend joining an ARTCC in your same time zone, as it would be easier to get training scheduled with mentors/instructors. Again, I can't stress enough that it is your decision and whichever ARTCC you decide to join, will be fun and enjoyable.