What is the best 2A3 SET Amplifier?

Best is very subjective. Here are some good choices (kit and assembled) at varying price points. The prices are list for new items. Shopping used can get you up to 50% off.

Bottlehead Paramour Monoblocks ($550 for kit)

AES SE-1 (Approx $950 as kit or $1150 assembled. Plays 2A3 and 300B)

Sun Sv 2A3 ($950 for kit, $1750 Assembled)

Bottlehead Paraglow Monoblocks - Parafeed ($1150 for Kit)

Wright WPA3.5 Monoblocks $1430

Welborne Moondog Mono's(Approx $1600 for kit or $2095 assembled)

Moth Si2A3 (Integrated) $1995

Cary CAD-2A3-SE Monoblocks $3500

Wavelength Gemini (Plays 2A3 and 45) $5000

I personally like Monoblock designs with tube rectification but you will get "heated" arguments over this.

Finally, do not equate "best" with higher price. This is not always the case. In fact, many DIY-ers will say that they can build themselves a home brew 2A3 better than anything that's out there for well under $1000 in parts.

My advice - Audition as many as you can first,check out local audio clubs and talk to the DIY folks.

Good luck

"Forget about the Cary, Wavelength or any SET amp that are made in USA(they are beginner in SET amp design!"

Funny - Last time I checked, it was the "novice" engineers in the good old U.S. that created the entire series of 2A3 and 300B tubes to begin with - oh about 70 or so years ago. You're saying that current crop of U.S. audio technicians and engineers can't make a decent SET Amps?

Go crawl back into your hole.