As I said above, I don't have a clear sense of which is inherently better. I own very low-powered versions of SET and pushpull amps, but they are not comparable in design so I cannot draw any conclusion. But, over the years I have made some general observations. First, the very best sounding triode tubes are all quite low in output power (e.g., 45 and 2a3), and using them in SET topology means one must have highly efficient speakers or use them only to deliver modest listening levels. By efficient, I mean something approaching or above 100 db/w with 8 ohm or higher nominal impedance). Second, as Atmasphere noted above, they need an air-gapped output transformer to deal with saturation and one can only partially offset the loss of inductance by making the core massive. This means the output transformer is usually very expensive; cheap SET amps with puny transformers sound whimpy to me.
But, with proper speakers and a quality build, SET amps deliver a very "pure" sound that can be quite seductive. While bass tends to be not as tight and punchy as that of a good pushpull amp, the bass has its own positive attributes--it has natural and subtle differences of tone while pushpull bass is much tighter and punchy at the cost of sounding a touch "mechanical" (sameness). I have no disagreement with someone finding the balance of attributes favoring SET amps. But, I do disagree with the "magic" qualities ascribed to SET amps; you can hear the same qualities in pushpull amps, perhaps not in the same balance, but there is nothing exclusive to SET sound.
We have not even considered OTL amps in this discussion. A well implemented OTL amp can have explosive dynamics and sound very vivid without being harsh or unpleasant as one might expect with that kind of dynamics.
