Anyway 300b & 2a3 cant power up anything much except very sensitive speakers with a relatively easy load to drive. Your limited on the speakers you can buy, Class D on the other hand can juice up even hard to drive loads with out issues or a change in the amplifiers character.
It also comes down to the speaker your choosing,
for me i choose speakers based on the amplifier i really liked. Which is usually the other way round for most audiophile.
I specifically looked for a 16ohm field coil speaker, The Classic Audio Loudspeakers not only fit the bill but sound more musically satisfying then anything else iv heard hence the reason why i stuck buy and bought another smaller pair the T3.4. They may not look pretty as other designs.
I also have the Line Magnetic LM3 Field Coils these are 16 ohms. I bought these just to pair it with the Atma-Sphere amps and it was out of curiosity but now iv decided to keep them too.
I love SET Amplifiers too, I am not just a OTL FAN! But OTL don’t bore me as much as some SET amplifiers, it musical and fast, its transparent and conveys all the musical emotions over to the listeners just like SET can do however OTL must be paired with the right speaker to transform your musical room to something really magical!