I use Amsoil Dominator synthetic in my 125. Never had a problem. My dad uses it in all his two strokes and they've worked great. Ran it in a SX 85 out in cali, put easily over 75 hours on the bike from brand new, and it's still running strong. I wouldn't recommend it for a break in oil on a new top end or bike, way to slippery. Run a good mineral oil to break the bike (or top end) in, then switch to the synthetic. But I don't have the money to do a top end every 10-15 hours on my bike, and I still run it hard, not a problem whatsoever. Maybe have 30 or more hours on it now and its still got tons of power. I hear Castor 927 is the best though. I have yet to try it, but I'd love to get some and see how it runs.
Hope for the best, Prepare for the worst.