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

For your hi-end Avantgarde 2.1, you should use the best 2A3 SET amp that money can buy.
Forget about the Cary, Wavelength or any SET amp that are made in USA(they are beginner in SET amp design!) - poor design, very low quality parts that including the output transformer!
*Cary designed a 300B amp that give out 15 watts/channel. I don't think the designer understands the 300B tube at all. It is a complete joke!

If you have the $$$, the best is:
Audio Note "Japan" 2A3 SET amp
JC Verdier 2A3 SET amp and similar 2A3 SET amp from L'audiophile

And remember always use NOS 2A3 tubes, please don't use any modern 2A3 tubes........

"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.

The Sun 2A3 amp is very highly regarded and reasonably priced.

The best sounding 2A3 SET I've heard is the Fi 2A3 designed and built by Don Garber. I drove a pair of Kochel horns with the Fi 2A3 monoblocks and the sound was nectar. RCA NOS and KR 2A3's sounded better than the stock Chinese tubes, and although the amps sounded great stock, I swapped the stock Magnequest OPT's with Tamura with a noticeable improvement. I demoed/heard most of the above mentioned 2A3's and thought the Fi sounded best. This is a VERY simple yet elegant design. Contrary to the above post, I heard Cary, Wavelength and Wellborne and thought they were excellent and well designed and have the utmost respect for Ron and Gordon, clearly not beginners. In fact Gordon Rankin and Don Garber have been harbingers in SET design and quietly pushing forward for years, well before SET's "came" into fashion. You have quite a few outstanding products from which to choose.