My favorite cocks are... the ones I can get my mouth on. Every cock I've ever had has been different so diversity in this is a given...
8 different cocks. 3 were similar to mine and what I would call average? 6.5" and medium girth. 3 were small. <4". 1 was long, 8" but no girth 1 was big, 9-10" and I couldn't come close to getting my hand all the way around it. All were oral only. Not really sure if I have a favorite, all different experiences. Some of them I've met up with a few times. My favourite times are when the other guy lasts about 10 minutes before cumming then doesn't want to reciprocate and just leaves. There's something about feeling used like that makes me very high.
I was looking at CaperRick69's numbers and I thought, "So many cocks over 61 years being bisexual. Difference races. Short, long, fat, skinny, cut, uncut. Oral and anal." Some are memorable; many not so much but I had the cock in some way and for the most part, everyone went away happy and if they didn't, well, I never tried to please everyone once I learned how impossible that is.
I lost track of the numbers, but 90% were in the 8-10" range with nice girth while the other 10% were in the 6-7.5" range. I do prefer the bigger cocks as they are more exciting for me to suck on, and I enjoy the challenge of eventually deep throating them; I love the look in their eyes when they see their entire cock has disappeared into my throat.