I believe the answer depends on two issues:
1. What is your price range for a preamp? As this will perhaps determine or limit the sonic qualities you are seeking.
2. What is your listening preference? Warmth and bloom and/or detail and transparency? Some to many tubes (in my limited experience) focus on warmth and 3-D bloom primarily in the midrange frequencies with light to serious roll offs at the frequency extreme highs and lows producing what what might consider a somewhat subdued sound. Whereas some to many solid state units focus on detail and transparency across a much greater frequency range but can easily lack warmth and bloom and may even be considered flat or suppressed in the very critical midrange region.
If your budget is very tight, and you are seeking detail over all else, you may want to entertain the solid state route first to see what you come up with. As your budget increases you should be able to venture more easily into either camp with fewer compromises that are supposedly typical of tubes and solid state but it's not a guarantee.
Again, my experience with tubes (and solid state for that matter) is quite limited but based on that experience and my readings, I believe the above to be true. Otherwise I'd change my opinion. :)
-IMO
