The 30-30 without a doubt. One of the best, and most accurate Handi barrels made. Get one you won't regret it. If you ever tire of it, sell it in the classifieds, it'll be gone quick. Can't say the same for the 06.
BTW, I'm not saying the 30-06 is a bad caliber, just that in a Handi, the 30-30 is a better choice. Unless of course your Sourdough.