Hi,

You need to realise that to talk about a given valve without context makes no sense at all.

The 12AU7 and 12AT7 are both considered "poor sounding" by many, especially by people who seem to claim 6SN7 "Ueber Alles", which in turn leaves me bemused, as the 12AU7 invariably sounds cleaner and more neutral than the supposedly electrically identical 6SN7, of course if you want traditional, cuddely, "low rez" tube sound that may be what you need.

In your Amplifier, in the context, in the specific circuit, with the specific other valves used (6SN7 & EL34 et al) the 12AU7 is in my view a better choice than the 12AT7. But that's just me.

Ciao T