Touhou is ridiculously popular among the core, but outside that, not many people know them
By sheer 'knowing' Mario would win any poll
Followed by characters like Link, Samus, Snake
Final Fantasy characters unlikely to be in the top 10 or even 20 simply because there are whole franchise lines who have the same protagonist
sales-wise, same goes. franchises > single installment in a franchise
vote heavily depends on who you ask
if you go and do that vote on the street and then on gamefaqs you'll get vastly different results
any list with a ff character in the top 10 is full of bullshit
the games are good, sometimes very good, but not so ground breaking ultra awesome that a character from a installment in a whole franchise could score top 10 in some sort of unrigged poll