300B SET vs.Triode Strapped KT150's???

What are the amps in question? I would say unlikely though in all honesty I have yet to hear the KT-150 tube. I will say however that to my ears tube rectification makes a big difference and sounds far superior to SS rectification. YMMV.

Hello freediver,
I’d say if all factors are equal i.e.builder talent, part and output transformer quality and attention to the power supply the 300b would be my choice. I just believe that it is the superior tube sonically. But variables do matter.

I would expect a well implemented and built to a high standard KT 150 triode strapped amplifier to out perform a mediocre quality 300b SET. Transformers and power supply quality are substantial factors with these types of amplifiers. More influential than the type of power tube selected. I’d advise to place focus on the level of implementation.
Charles,

Freediver ...Since the sound of the tubes is fundamentally different between the 300B and KT150 tubes, the rest of your circuit would need (as they say in the fine watch world) "complications". Why not avoid adding what isn't there and simply embrace building a 300B SET amp? There are several excellent kits including ones from Audio Note Kits and Bottlehead. ...Or, you might find a completed kit or commercial 300B amp here in the classifieds. 

I'm currently listening to three different tube amps: Rogue Cronus (KT120), Ayon Audio (KT88) and Raven Audio (6L6). They could not sound more different, and in the case of the Raven (6L6) and Ayon (KT88) amps, it's the tubes. The Rogue is a very good amp also, but at that price point there simply isn't the level of components due to cost burden. I have listened to 300B amps and they do sound glorious for some genres of music. (Eventually a 300B amp will appear from a UPS package as part of my personal education.)

Vicweast,
If you get a high quality 300b SET and use appropriately efficient /sensitive speakers you'll discover that you can enjoy virtually all genres of music reproduced at a very high quality level.  This has been my pleasant experience the past 7 years. 
Charles, 

this is my dilemma atm. Looking at a bunch of mid price SET amps this week, torn between the 300b and kt150

You are trying to compare apples and oranges.  The KT150 tube, "triode strapped" or not, doesn't sound anything like the 300b.  I assume that you are considering a 300b SET and not a 300b amp in PP configuration? 

There are practical implications beyond the obvious sonic differences: a KT150 amp is going to be PP design, putting out more Wpc and many (most) will allow the use of 4 ohm speakers.  Almost all 300b SET amps are going to be 8 Wpc channel or less, and most will provide 8 ohm taps to the speakers.  So your speaker selection is going to be critical to the success or your choice of amp.

My suggestions is to choose your speakers first, then find an alp that works and sounds best with your speakers.  Doing it the other way is putting the cart before the horse...