Sonic atributes ultralinear vs tetrode vs pentode

What are the sonic attributes of and amp running in Ultralinear vs tetrode vs Pentode. Looking to get a new amp, but live in a rural area can't audition them all. I don't like what I have heard from Ultralinear amps, too hard sounding for me. A lot of new pentode amps on the market, can't audition any. Why pick one over the other?
Thanks
Mike