Guts is solid. Their greatest selling point is that their free spins carry no wagering requirements i.e. whatever you win from free spins is cold hard cash.
They also have very quick, 2hours or less cash out times, no pending peroids.
I think you should stay away from flash altogether because on mobile devices i.e apple iphones & ipads, flash wont load and where the flash player is supposed to be you'll get an error looking message informing the visitor that they need to download flash. it'll look hideous and not worth it...