Thing about "popular spots" is that it leads to people fussing over who is considered for what. That is, like the argument over Juri was that she gets too much upper body stuff when she should only be tickled on her feet due to being a "foot fetish icon." Now while I don't know all that much about her, I do know that she's also known for wearing very little from the waste up as well, so it'd seem to me that there's plenty of her to go around.
But then "popular spots" gives way to "my favorite spot" usually, particularly in regards to the most popular among the fetish. Tifa for instance is in the running for most tickled video game girl and I don't need to tell you what she's known for, though she does get a lot of armpit focus now too. But of course a majority of her art is feet because that's what the majority likes, regardless of it it 'fits' her.