It really depends on where your at with parts.. If you have a set of stock cylinders that arn't ported.. I'd go with the stock cylinders.. But if you have to get new cylinders.. then get them ported.. your farther ahead getting a cub. Both will run very close. It really comes down to setup... Both will be fast.. as long as their setup correctly for what your doing.
Talk to some builders and ask them wich route would be better for you, your expectations and budget.
A&S and RDZ build some VERY fast stock cylinder motors..