I think the Studio Projects mics fare a lot better than their preamp does. The C1 is a little hyped for my taste, but the B1 sounds good, and the TB-1 very smooth.
The vtb1 is obviously the least expensive pre of the bunch, and it really shows. The only pres I wasn't impressed with were the vtb1 and the Speck. Everything else seemed to take turns having it's moments, but nothing really stood out head-and-shoulders or anything on a consistant basis.
The differences were so subtle, if I had to pick one, it would probably be the Phoenix Audio (I remember liking more than a few of the tracks with it in particular), but I'm sure I could make some perfectly good recordings with any of them, including the Studio Projects (if I were held at gunpoint).