My favourite is AD825, it is single, stable starting from G=1, and 50mA capable. Great soundstage, no veil, very musical, impactful, no harshness, colorful but not colored sound. There is nothing better IMHO. I suggested one guy to use them, and he discarded from his amplifier 2x OPA627 for those AD825s. Another happy guy!
I heard all chips from balou's list except JRC4558 and LM4562. So...
NE5532 - the only good is from Signetics, all others suck
LM6172 - very nice, impactful, clean, dark, some people find it cold
OPA2107 - dark and laid back sound, very deep soundstage, not so broad
OPA2604 - a bit like a tube, rolled off on both ends, a bit boring and too rounded for me
OPA2227 - terribly laid back, bass heavy, veiled and slow. Completely not my type
OPA2132 - almost like OPA2134, maybe a bit smoother sound. Generally - tubby bass, mediocre soundstage, recessed subbands of the midrange and not very detailed treble. Nothing special.
NJM4556 - sounds... funny
Nice sound but I don't know why it sounds funny to me. Smooth sounds with long decay, no harshness. I haven't listened to this one for prolonged time.
AD8066 - good soundstage, a bit narrow, big bass, veiled midrange, nice treble and overall caramel sound signature. I like it
AD823 - a bit harsh making it perceived as detailed, but it is not very detailed. Weak impact in sound, rather analytical. One of the noisiest I know. I don't remember all details well because I found better chips later soon.
AD843 - impactful and harsh, sometimes it's getting unpleasant. IMHO tangensoft overrated it saying it's around OPA637's class. It is not. Too unnatural.
AD744 - very natural in color and soundstage which might give impression as present everywhere. What I dislike is its relaxed and therefore "dead" sound. However some people may like it.
AD8620 - good impact with quick and punchy bass, very good soundstage, not spectacular though, slightly harsh and slightly veiled - kind of a nonsense tradeoff. Some people find its highs too aggressive, I don't.
OP275 - like V-shaped equalization curve, bass up, treble up, recessed mids, overally good and just nothing special, simply good, maybe very good.
OPA2228 - uncompensated alter ego of OPA2227 but totally different. deeper but not muddy like 2227's bass, actually very nice, lots of air in midrange and silky highs. Warm and natural. Just slightly laid back with delicate veil which pairs well with 2228's airy presentation. Electric guitars and female vocals sound nice and intimate. Very likable chip, but not for low gains. You can compensate its feedback loop with capacitors, but I don't like this method and find it degrading the sound a bit.
TLE2082 - many times my favourite but no longer. It's like unveiled, more metallic in treble and less harsh AD8620, better and clearer soundstage, punchy and filled up bass. This chip is more on the bright side.
TLE2142 - sounds dark, with well detailed highs, strong and precisely articulated bass but not as filled with mass as AD8066. You may find the midrange a bit loosing color, but soundstage and its deepness is ver good.
AD797 - is like more analytical version of AD825, less impactful and with some glaze over highs.
OPA637 - very natural and detailed in the whole spectrum, preserving all music singature besides life. For me this chip is uninvolving. It's good for analysing music, not listening for pleasure.
AD8397 it is power hungry and truly powerful. 310mA peak makes sense as a true amplifier. However you need efficient ground channel to keep AD8397's pace. It is a bit bright, very close soundstage, almost like being between performers. Short decay, overally gives impression of being transparent but it's a bit on the bright and smooth side. Comparing it to be more efficient than 2x BUF634 gives it overall high rating. You can use AD8397 as a dual buffer because it is unity gain stable.
I think, that's all... Is my liking non-standard?