I would definitely go for RB.
The 353 has better top end compared to the Flash 12 but less bottom than the Flash, so basically they traded each others bottom and top ends.
RB engines are made in the same place as Novarossi, only they are made to RB specs so in my eyes they might be slightly more aggressive in terms of port timing.
Since I changed to RB, I don't think I will ever change to anything else, ever. They run as cool as ice, provide HEAAAAAPS of power and will last nearly forever!
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"