I've had high strung engines such as Conley, Abitar, OPS, YS, Fitzpatrick Bros. and others, the only problematic performance engines I've seen are the YS. Other than YS, I can't think of any to stay away from. I've never owned a Rossi but know that they are quite reliable, Jetts are very reliable. So, where is this imaginary choice you're looking for?

Fox engines are very reliable as are MVVS and as to Diesel I have them from an LA .10 to a SuperTigre 4500 and all throttle cleanly when the carb is set correctly.