"Best" is all relative to what sonds best to YOU. What sounds best to me, might sound like crap to you. If I were in the market for a strictly blues amp, I would most likely look for one that was powered by 6L6's, no more than 50-60 watts, might would also go with 6V6's to get the watts down, so I could get the tubes crankin' without killing my ears. I'd probably go with a 2x12 alnico speaker setup. No master volume (will use an attenuator if needed), one channel with volume, bass, mid, trebel, and reverb control. Tube driven reverb unit, and that's it. I would also probably try to search for an old Fender delux reverb. The Bassman is also a lovely blues amp, along with a Marshall JTM45.

Most importantly, it depends on what sounds best to you, and what you an afford to spend.