avantgarde loudspeakers

I think it's a little simplistic to say that DIY is a better way to go. For the vast majority of people it is not. You need three things to accomplish DIY successfully: Time (alot of it), knowledge, experience. To think that you just buy some various parts, find a simple DIY diagram, and assemble a SOTA system that can compete with or eclipse many commercial products is silly. If you have the above three criteria met, great, otherwise DIY can be a frustrating and expensive lesson in humility. Then again, it may not. I'm not a gearhead, as you can probably tell. BTW, I would love to have the time to learn to do DIY but have other acitvities that are higher priority (career,family,etc.).

I had both Duos and Trios. Unless you can be pretty far away from them, you hear parts of an instrument coming from different places. Also only with the flexibility of the Trios could you get both good bass and good imaging. I have had the Beauhorn Virtuosos for better than 2 years and love them. They use one driver, the Lowther, and have no crossover. They need help on the bottom, however. They would probably not be considered as pretty as the Avantgardes, but are smaller and cheaper.

I have the current Duos, driven by by my rebuilt Quad IIs, Verdier Control B tube preamp and fronted by a Platine Verdier, Schroeder Model 2 and Allaerts MC1B.
You need to set the AG horns up properly - toe in to focus in front of your listening seat, and adjust the bass roll off and sub woofer volume correctly. Get the Subwoofer wrong and they can sound really unimpressive. Get it right and it just clicks.
I've heard Lowthers in any configurations, but they're not the same. In my previous life, I worked selling HiFi with Ken Kessler, before I became a medic. Like Ken, I like my system to have plenty of dynamics (I'm also a Decca fan) yet have the lucidity of tubes. The AGs are my best ever purchase, even better than my original Garrott Brothers Decca cartridge.
The AGs cost a lot as the horns are machined to very fine tolerances, so not a great DIY prospect.

Agree with tbg and topoxforddoc. I listen to my Duos about 12 ft. to the sweet spot. Listening distances < 8 ft. is not advisable. You need that extra distance for multiple driver integration which becomes seemless causing these large speakers to disappear. The crossover between the midrange and bass unit can be problematic but with careful positioning and adjustment, this can be eliminated.
In terms of being the best, that is obviously a personal judgement. All speakers have compromises, even SOTA designs. Whether you prefer horns,cones,electrostatics,single driver speakers is up to you. As to horns, the AG's do not have any classic horn colorations such as a "cupped hands" sound. Out of the commercially available,full range,> 100dB sensitivity speakers, I liked the AG's the best. I've had them for 2 years and don't regret anything about the purchase. AFAIC, I've found the speakers I plan on keeping. Highly recommended.