You wont get any criticism for those 2 engines.
Really you cant go wrong with either of the two, they are both comparable, but I would think that the Flash PT '11 would be the stronger engine - being newer and all IMO.
I think Max Power engines are like RB - meaning they are made in the same factory as Novarossi, but to Max Power specs (I could be wrong there, but RB has their parts made to RB specs)
Car-less (Velox V10 or 733) // RB T10.5"+" (JB Modified) // Bluebird BMS-990DMG (St) & BMS-631 (T/B) // ATS 16% // Capricorn Wheels // Protoform
"70% of the time, it works ALL the time"