Apart from considering the specific models of amps, there are many listeners who adore the sound of amps running 300b tubes. I will agree that the midrange, in particular, of 300b amps sound saturated and beautiful. The upper bass/lower midrange prominence also gives that tube an invitingly warm sound. But, for others, like me, the sound is a bit too lush and warm and amps running that tube tend to sound a bit "polite" and lacking in punch and micro-dynamics.
The 45 tube offers, in my opinion, a much more neutral tonal balance, and has a much tighter lower bass than the 300b, and is a more lively sounding tube (apart from the lack of power output). I own a push-pull 45 amp and I like its sound a lot.
I also own a parallel SET 2a3 amp (Audio note Kageki). I've run NOS RCA, EML meshplates, and EML solid plate tubes in it. I like the sound, but, 2a3s do tend to be on the lean side (thinner upper bass than the even the 45 tube). My Kageki amps are on loan to a friend who will be converting them to running on 45's because we both like the sound of 45's.
I have heard Korneff amps and I liked the sound and the build quality of those amps. I've heard Sofia amps that sounded okay (not bad, but not standouts), but I wasn't that thrilled with the construction. But, overall, I think the choice comes down to personal preference and there is no way to say whether one will like one sound over the other. I know a lot of people who will take a 300b amp over any other type of amp because of its glorious midrange, while I prefer the 45.
I like many other tube types and topologies as well. The amp I currently run in my system is a pushpull amp running 349 pentode tubes; I like this amp a lot. I also like many amps that run 6L6/KT66 tubes. The amp I think is the best I've ever heard is a custom-built output transformerless amp running a television sweep tube of some sort.
