What's the greatest bargain in SET these days?

Rebbi,
Some level of NFB may be necessary depending on the speaker you choose. NFB will I believe result in a lower output impedance for an amplifier(and likely increase the damping factor, DF). This is advantagous for some speakers.Most SET amplifiers use DHT tubes which are inherently linear and don't require NFB as pentode tubes and transistors often do.Some speakers are designed to mate with the SET amplifier's higher output impedance and thus sound terrific. SET s have very straight forward simple circuits and many of their builders feel NFB will hurt the purity of these simple circuits.Most push pull pentode type amps aren't linear and will gain sonically with "careful" NFB use. It just depends on what you're trying to achieve and proper amp/speaker characteristics matching. In short a KT88 might need a bit of NFB, A 300b or 2A3 can get by without it.
Charles

Good stuff!!!

Very helpful and informative, guys, thanks!

Rebbi,
It's nearly impossible to judge and rate amplifiers without knowing the speaker in question, their linkage is that vital. A fabulous amplifier can sound bad with the wrong speaker choice. The same is true of a wonderful speaker with the "wrong" amplifier. When people use the analogy of a good marriage to stress this point, they aren't kidding. Honestly, NFB can be either desirable or detrimental depending on the circumstances. In my "individual" case, I get along without it very well.
Charles,

@Rebbi, I have a VAC push-pull tube amp that has adjustable global feedback from 0-5 dB in 1 dB steps. The manual recommends trying them all as it is simply a means of matching the amp to the speakers. Sort of like trying various output taps or tubes.

I tried all 6 positions and found that my speakers sounded best with the 0 dB feedback. As I increased feedback, I noticed more high frequency detail, but at the expense of rhythmic bass drive. The music became thinner and drier.
Who knows? Maybe if I change speakers some feedback may sound better. It is all about amplifier-speaker interactions. I do think that it is a nice feature to have though, adjustable negative feedback, as it does allow for some wiggle room when matching amp to speakers. I wish more amps had this ability.