Do you have a favorite nipple shape? My type is almost without areolas. Protruding points.
Ah, the question of nipple geometry, if you hadn't asked god himself would have had to.
Before one can even begin to broach the question of favorites it is imperative that we classify the species and character of nipples that are available. I will for the sake of brevity keep this endeavor to human female nipples even though the array of nipples and nipple analogues available in natures do not begin and end with the delightful ornaments that perch atop the human female breast. Additionally I am taking for granted that "nipple" in this case refers to the entire nipple areola complex and not just the central fleshy protuberance.
To some, perhaps the most provokative element of the nipple is the nipple itself, and of more precise relevance to my analysis is the level of protrusion both at rest and in full tumescence. Nipples can range in "elevation" from the surprisingly positive nearly dactyl to the tropophobia inducing negative rise of the inverted nipple. While I am appreciative of any intimate contact that breast owners choose to provide me, I do harbor a platonic ideal in this arena. I believe that it is less important that the nipple protrude some certain amount (though some protrusion is ideal) than that the ratio of nipple protrusion at rest to protrusion at peak concupiscence be significant enough so as to be noticeable at a glance. This is of course an aesthetic preference, but it is also practical applications. If one relies on apparent physiological responses to tune their sexual exertions and erogenous manipulations then an easily intelligible nipple response is a boon. This is of course should never be the only metric, and discussing sex with your partner is likely to be the most informative route, but sometimes pausing to ask 'Hey, do that feel better when I lick your butthole like this or like this?" is the least sexy option. Not that I would know from personal experience, as I've famously never had sex because I can't figure out how to do it without risking wet stuff splashing on my skin or god forbid getting in my eyes.
Next let us move onto the areola, the seat of power from which the nipple benevolently reigns over the breast. Areola can vary in circumference Swell or puffiness, surface smoothness and level of hirsuteness. Once when I was a younger man I was doing some heavy petting with a young lady, and just as we were progressing to the shirt removal step of out little dance she stopped me, she became very serious, a little ashamed even. She warned me that her nipples were hairy, I wanted to laugh but I knew she would mistake what it was that I thought was funny. You see, there I was with a boner that could easily pierce the chobham armor of a modern tank, about to see real live titties and she though that I might think twice about hair on her nipples. To me it was funny that she even considered that I'd be anything but pretty stoked to touch a titty, two even. Anyway she took her shirt off , and I brushed my fingers across the few little blonde hairs on her nipple and watched them rustle a bit when I blew on them. Her nipple git hard, and I think we both found it to be pretty sexy. All that to say I wouldn't put "Must be hairy" in my idea nipples box, but I don't know that a little hair would be unwelcome if it made a surprise visit.
So, What is my favorite nipple shape....the one on the titty on the person that is excited for me to put it in my mouth.