Between the two you list, the Norvell is the one to go for. The TT is under powered.

It's no accident that you don't see the top guys flying the TT pro .25 at the big contests.

Engines you do see most often (in no particular order, and I might forget something)

Norvel (both BB and Big Mig)
OS FX
Irvine
Webra (new engine, MAJOR power)
Mag .28 (but ignore the .25, it's underpowered, and over weight)
Jett .30 (less common, expensive, but hard to beat)

Whatever engine you get, you'll want a mousse can or ultrathrust muffler to go with it. It's cheap and easy power.