12CC's room is a big room with a real stage and rows of seats, so the atmosphere is more like a concert than a coffee house. The TH's room is a real art gallery, so it's clean and modern and not restaurant-like.
The Net and Catacombs CH are run on church owned properties of one sort or another, and you'll find that about half the clientele comes from the church membership. That's ok, it's just where the coffee houses do their best advertising. The music is occasionally Christian, but I've been introduced to a wide range of local talent at these places, and the coffee houses located in churches may be the most varied in their lineups. The musical atmosphere is very informal, with open mics and flexible scheduling.
The bookstores have their own, well-lit but sort of trendy atmospheres, and they are commercial coffee houses, so the coffee is OK.
For the real coffee house atmosphere, you have to go to the commercial coffee houses (Little Theater Cafe, Colosseum Cafe, Moonbeans, Java Joe's). I haven't been to the West Coast Cafe; is it even a coffee house? The commercial houses have the best coffee and desserts, of course.
Having said that:
Dynamic's open mic was cool. A very cheap way to get a nice recording of yourself at the open mic. However it is on hold for now.
If you're looking to meet babes (or guys), we think the coffee house scene can serve you as well as any other social venue. Of course, the smaller venues (CCH, Java Joe's, The Net, probably West Coast) may serve you better than the larger venues (12CC, LTC), since the larger venues tend to draw couples. All of the venues that feature multiple acts (mainly, all but the book stores) have intermissions, so there is an opportunity to mingle. You can get to know a whole bunch of people pretty well by simply attending performances week after week, so pick the music you like, pick the venues, and don't be shy.