2a3 ?

I like 2a3’s, provided the speaker is efficient enough.  The. 300b tends to deliver a richer sounding midrange and a warm bump in the upper bass that is part of the “magic” of that tube, but, compared to the 2a3, the 300b sounds murky and not as dynamic and alive.
At even lower power, there is the 45, which sort of fits between the two.  It is not as lean sounding as the 2a3, it delivers deep bass (but tighter and punchier than the 300b), good dynamics, and almost as much clarity as the 2a3.

I have both! A Will Vincent custom- built 45 SET using Emcron output trannies; a 2A3 Sanei 560A with Tango power, choke and trannies from Japan. Neither in use because I sold my vintage Heresy's - the only speakers on hand capable of use with low power SET's. The 45 is only good for 1.75 watts at clipping; the 2A3 will do 3.5 watts. Subjective impressions of these two tubes is entirely dependent upon speaker choices. In fact the 45, 2A3 and 300B are most linear when used at 25% power. Past that distortion rises rapidly!

My speakers are 99 db/w efficient.  I own a pushpull 45 amplifier that works well with these speakers, but, I don’t play music that loud so I can’t say how happy others would be with my setup.  I have a parallel single ended 2a3 amp that also delivers sufficient power.  My favorite amp is a pushpull 349 (this is a very rare tube that, fortunately, has a long life when driven gently) amp that delivers about 5.5 wpc.  

I had a wonderful Tektron amp that used 45, 2A3, and 300b.  I think the 2A3 might have been best but it depended a lot on the tubes.  Jerry

I own the Coincident 300b stereo and am very happy and impressed with it. I did upgrade the tubes on my own.