If you're looking for a human-power answer, consider a scrub and Jack plane. Works great for me. Doesn't hurt the flab much after a while.
I do what will become the bottom, since I draw my circle up top. Usually less wood there, and it also provides a firm platform for use of a circle jig and for trimming the ends at an angle for weight and balance, as well as making sure that I'm getting the best diameter I can out of a piece with a tool a bit more capable of making a fair circle than my chainsaw. What's up top isn't too important before roughing, and I can also cheat a bit and gouge out heart checks so they won't grow, knowing that the sides will retract anyway.