for bjs, SMALLER. gah. i get cockjaw and have to stop after a while. The Husband gets frustrated when i'm unable to finish, to which i reply, "gah, it's not like i can unhinge my jaw like a freaking rattlesnake!" a perfect cock for a bj IMHO is one that has a tapered head and is only as girth as the shaft itself.
for fucking, larger. i used to have a bf who could make me ejaculate just from his huge head. we had to lay down towels beforehand. but i was never able to blow him really well nor could he penetrate me deeply b/c it was like getting nailed with a baseball bat.
i think guys should just come with inflatable cocks.