I'm looking around for a good card company too.
I used Vista Print a couple of times, but I'm not going back.
Pros: Vista Print is very fast, and cheap. They've got a big design selection also.
Cons: Vista Print's cards are cut smaller than ordinary business cards. You also need to be careful at the check out process - they like to default you into ordering additional things if you're not paying attention to what you're agreeing to.
I use my vistaprints cards if I am going to be in a situation handing out cards willy-nilly; wedding fair, leave a little stack on a table at the reception, etc.
For giving to clients at meetings or random people I meet day-to-day, I use
MOO. More expensive, but worth it.
I use 30 or so different images for the backs, with one image on the front of every card. Very high quality, eco-friendly, great service and timely turnaround. Plus it comes with a neat little card holster.