This will undoubtedly start a big debate and is still highly opinionated even after the guidelines you've given. You'll get a vote for every single one of those as they are all decent engines but I'm gonna bet right now you get the most votes for novarossi or RB (provided the 2009 engines are the same quality as the last seasons before Rody left the company). I searched for several months last year and decided for my budget a RB S5L2G but don't have the money this year being laid off.
The only thing an RB won't meet for you is the piston/sleeve is something like $125 but you should get 7-10 gallons out of it if you treat it right. Good luck
