JustJess said it perfectly (I swear I already replied to this!). It's all about proportion for me. Velvet-wrapped steel is an excellent way to put it.
I am really not a fan of enormous (had one boyfriend in this department - holy crap that hurt). It's very limiting for me - hard to keep teeth off of, painful or super slow anal, just very slow and careful all around - get's old. I guess this is a case where "average" really is spectacular.