Hello Thomas,
Welcome to VATSIM and VATUSA. Picking an ARTCC to join can be a very personal thing, as each ARTCC has it's own 'flavor' The members of the ARTCC are as much a part of it as the airspace itself. Many people choose the ARTCC based on the airspace they are familiar with (i.e., home airport contained within, favorite arrival/departure airport, etc.). The requirements you have indicated creates a pretty narrow window. Popularity often (but not always) brings complicated procedures to keep all the traffic safe and orderly. And then you also have to look at the Instructor to Student ratio to ensure you will be able to receive the training needed to advance in the ranks. Of course, once you get your initial rating assigned you can visit at other ARTCCs vary your experience for traffic levels and airspace.
The best advise I could give without making a plug for any one ARTCC would be this. Choose the ARTCC which covers a region where you most feel at home because often times the majority of the controllers will also be from that region. Then as time goes along visit other locations. Who knows, you just might find another location you enjoy more.
