What's the best EL34 amp besides 8b?

The Dynaco was introduced in 1959, and over 350,000 ST-70's had been sold when production finally ceased, making the ST-70 the most popular tube(not just EL34) power amplifier ever manufactured(though perhaps not, "the best."

The ST-70 is a good amp, but at full power the 5AR4 rectifier is under stress. They should have designed it for a pair of them.

There is an excellent thread on the ST-70 design over on Audiokarma.

Gianttube, in case you might still be reading this, another perspective.

I don't believe there is a "best" of anything. Any component is dependent on match up with the remainder of the system.

Now if this is of any interest, I recently bought EL-34 based amps. I began my audio hobby decades ago with a Dynakit ST-70. Later I owned the famed 8B, followed by a Music Reference RM-9. I considered each of those to be a step up and I always admired the musical mid-range of the EL-34. My recent purchase was a pair of Manley Snapper mono amps. The retain that mid-range charm but offer a more extended frequency response, particularly in the bass. However they have 4 outputs per channel and 100 watts which may exceed what you are looking for.

Much ST-70 improvement can be realized by dropping the power
supply's impedance, via added capacitance(within the
rectifier's current limits). Joe Curcio helped me extensively
work mine over. The tubby bass and peak compression, common
to the 70, were gone. That was noted and followed by a number
of upgrades on the driver board, input/output connectors and
power cord. All mods were accomplished without
modifying/cutting the chassis. A second/paralleled 5AR4 &
heater transformer, wouldn't have be hard to implement,
perhaps included in an outboard power supply. That was all
late 80's/early 90's. I got power hungry and went to Cary's
SLM-100's(now worked over too). I still miss the 70! It was
a ton of fun!

There was also the ST70 II manufactured by Sound Valves and sold by Pancor that used solid state rectification, bigger output transformers, and and a beefier power supply than the original. I think that it's a really good sounding amp, looks great, and was pretty reasonably priced (especially when closed out near the end of its run). I still have mine, tho I haven't fired it up in several years.