I don't usually mind how they mention it. They could do it as two characters meet face to face, noticing their eyes or seeing their hair. The narrator can just jump in and tell me too. As long as it doesn't take up the whole story. I think maybe 2 or 3 lines to describe their exterior is fine in actual physical features such as hair and eyes and muscles etc.
Personally I don't like it when the first person describes someone, especially when they're talking about their love interest. I also prefer it when they just tell me what they look like. It annoys me when they try to make it subtle; it makes it cheesy and horrible to read. Just tell me that she has brown eyes that were slightly slinted, especially when angry . . . Not that she brimmed with rage, her sharp chocolate brown eyes poisoning anyone who crossed her path. Ugh . . . I hate the word chocolate when describing. Itรขโฌโขs okay to use that when youรขโฌโขre not describing eyes, no need to mention the chocolate brown, or even the sharp in that case. But I won't stop reading because of it.