Which is the best single-ended tube amp

Art Audio makes superb-sounding, gorgeous products, very affordable by SE standards. KR tubes, super transformers. They've received more rave reviews than anything else in the past year. Most recent is the review of the 20 wpc Jota, $7500, on soundstage.com. It's very well written and articulate, and right on the mark! The 13 wpc Diavolo is $6000 for 13 BIG wpc. Yes, I've had it in my system, and will acquire one. These amps exist at a level way above the normal hubbub of blah-blah what's best. They are a new paradigm that you can live with for a long, long time. Note the Stereophile June 21 review, and soundstage.com, September, that found Silverline Sonata and Sonatina to be exquisite with SEs, including the Art. Please visit the website, artaudio.com.

BAT VK-60 and the 50se preamp sound exquisite and make seemless sound.

Depends how much you want to spend......but you just can't go wrong with Audio Note [UK] one of the oldest and most reputable English manufacturers. See their website at Audionote.co.uk. They do great kits as well. I have a 7W stereo Conqueror which drives speakers really well.

Blue Circle BC 2000 hybrid (tube/ss) monoblocks. The best of all worlds in two wonderfully weird upright boxes.