| What are using it for?
The cheap "tube" preamps (ART Tube MP & Tube PAC, Presonus BlueTube, etc.) use a starved-plate design for the tube section, which works to add grittiness to the signal when you want it, but doesn't really provide the true tube character. Just because it has a tube inside the box, doesn't mean it's "warm" or "tubey" or whatever.
The EHX 12AY7 Mic Preamp has gotten some pretty favorable feedback on some of the recording forums. It uses a full-voltage plate design for the tubes.
My current favorite at is the ART MPA Gold. The stock tubes are pretty crappy, but swapping for a decent set of JJs or Mullards really brings the MPA Gold to life. I'm LOVING it for recording bass with a Radial JDI in front of it - very warm and fat. I've heard good things about it as a vocal pre as well. (Note - The MPA Gold is not the same as the MPA Pro. The Pro uses a starved plate circuit for the tube.) | 
