A seriously subjective question, but an interesting one. Consider checking out a Kevin Deal video on Upscale Audio's site. He talks about tube power amps and preamps, with some discussion relevant to your question. He ultimate suggests, as a "reasonably" priced system, the McIntosh MC275VI matched to the PS Audio Gain Cell Preamp/Dac. His argument is that you get "some tube glory" from a tube preamp, but the significant tube effect comes from the tube power amp.
