While the Model T is a great amp, if I wanted some serious head distortion I'd probably go with an Orange or a Hiwatt, but that's just me.
Orange yes... but Hiwatt?
IMO Hiwatts are just about as clean as it
gets, unless there's something wrong with them.
I'd say Orange, Matamp, even Marshall if you want big raw
nasty power.
If harmonic distortion is the goal, I'd avoid Dave Reeves (Hiwatt/Reeves) and Dynaco (Sunn) circuits, unless you use pedals or overdrive the preamp stages pretty hard.
Both of those circuits are pretty Hi-Fi, but generally take pedals quite well.
Just in my opinion, of course.