I used dino oil for break in of two tanks. I think it's important to run the throttle a third of the way in for 15 min, then let it cool for 15... run it two-thirds of the way for 15 min, let it cool for another 15... run it WOT for 15 min, let it cool for another 15. I also think letting the engine warm up and not going WOT immediately after cranking will help the engine out.
Anyway... I'm using Klotz Super Techniplate as most dirt bikers seem to think that and Maxima Castor 927 are the best. It's 80% synthetic / 20% castor. Both of those oils seem to be better than dino, but synthetic seems to be a tad bit better than castor, but castor still has its benefits... so a 4/1 ratio of syn/castor seems good enough for me.
Rocky Mountain ATV seems like the cheapest place to buy the 2 brands mentioned above.
Beware that some people believe that once a jug of castor oil is opened, it's only good for a week or two. I dunno if I believe this or not, but I might be switching to Amsoil as I just found out a friend sells the stuff. He also says that no petroleum goes into Amsoil, which I thought all synthetics used oil as a base stock... but since Amsoil *was* the first syn oil manufacturer, maybe they do have it figured out to where they don't need any petroleum.