AMSOIL all the way! Mixed 50:1.
You're gonna get a TON of opinions on oil.
Run a name-brand oil made for 2-stroke atv's and motorcycles. DO NOT USE OIL INTENDED FOR OUTBOARD MOTORS AND/OR WATERCRAFT!!!!!!
As long as you use an oil that meets JASO FC or FD and ISO L-EGC or L-EGD standards, you're good. You'll see a section on the bottle label where the oil certification is printed. Yamalube, Bel-Ray, and AMSOIL are all certified.