I really loved my college boyfriend's cock that had a huge head and was thicker towards the head than at the base.
The other big dick I really loved had a pretty big head but got thicker toward the base because I could really feel that opening me up as he got further inside me. I actually think this felt the best, but I agree with some of the women, it's a little hard to recall exactly and there are other elements that go into good sex. I really did enjoy the feeling of being filled by both these boyfriends.