My preference is any oil sold as suitable for a two stroke transmission. We even used zero weight oil in our race bikes a while ago - transmission fluid - clear color.
I usually use Honda's Hp trans oil
http://www.ebay.com/itm/like/3913815345 ... noapp=true" onclick="window.open(this.href);return false;
or Silkolene from Fuchs.
http://www.silkolene.com/motorcycle/gea ... oil-light/" onclick="window.open(this.href);return false; or
http://www.silkolene.com/motorcycle/gea ... comp-gear/" onclick="window.open(this.href);return false;
MOTUL and others have similar products.
People argue that for our transmissions, almost any oil is better than what was available back in the day and we hardly stress them at all and they have a point, but when I am wringing it's neck changing gears at 8,000 plus with an air shifter at full throttle, I think I should use good oil. Oil is cheap and you use say 2L every year, how much do you save/waste by using cheap/expensive oil?
It's a personal thing. Whatever you decide to use, it will probably be just fine.