I would split "does penis size matter" into two questions because it most certainly matters when the goal is reproduction and most certainly does not when pleasure is the goal.
Personally, I'd like a smaller penis, but I would agree that there's some selection pressure for a large penis.
Dawkins discusses possilbe selection pressures on human penis size, as well as the evolved lack of an os penis in humans, in "The Selfish Gene" (second edition preferred, as it contains more discussion on the topic)
In a discussion about how the lack of an os penis (baculum/pizzle) could lead to the penis becoming a diagnostic of health in a male he states, "It is not implausible that, with natural selection refining their diagnostic skills, females could glean all sorts of clues about a male's health from the bearing of his penis."
As far as what's better for receiving idk why there has to be more to it that "I like big dicks" or "I don't really care." As far as giving goes, well, as long as it fits? We can't exactly ask directly and I doubt anyone out there is running formal experiments measuring hormone levels and muscular response, so we just have anecdotes of body language and behavior that appears to show preference. Beyond "Never had a problem, she seems happy" it just kinda devolves into a pissing contest.
