Most desirable vacuum tubes for SET amps

+1 testpilot. Any one of the listed tubes can sound truly excellent if careful attention is given to speaker selection. The higher power transmission output tubes such as 845 and 211 can be magnificent  sounding in the hands of a talented/skilled builder.

Same is true of low watt 45,50,2A3 etc tubes. Ultimate results are fully dependant on the designer/builder and quality of the parts utilized. I just do not believe that any one single tube can be declared the absolute best. There are a multitude of factors to be considered.
Charles

yep, the best one is the one that sounds the best to you, the best implemented in the amp, the best matched to your speakers, to your room...

asking these questions -- what is the best speaker, what is the best dac, what is the best cable

ugh

Thanks everyone for these wonderful responses. I feel, 300B got a cult status & many folks are waiting for another batch from Western Electric.

on a side note, I didn’t ask opinion for ‘best’. I’m looking for opinion about desirable tubes. The ‘one’ which everyone is after. It could be for academic purpose.  Need not be the best. Again, it doesn’t matter whether it sounds the best in my system. The desirability has nothing to do with it. It’s what the general public ‘wants’ !!

Many swear by NOS 300B Western Electrics. But they have become rare and upwards of $5000+ a pair. My favorite are 45s in general the lower the power the more magic. But at 1 1/2 watts you need super sensitive speakers.

Again no clear cut answer. Most desirable to who? One could certainly say the 300b is the most popular DHT tube. There are numerous current production brands (With various price categories to choose from) 300bs available. A sign of demand if nothing else. There are probably more 300b amplifiers produced than with any other DHT tube. As has been pointed out, the vintage/original Western Electric 300b is highly coveted and extraordinarily expensive. So to a certain niche of W.E. tube seekers  they are very desirable.
Charles