Hmm.

For me, I think its Wind. Kushina Uzumaki [Red Hot-Blooded Habanero], Minato Namikaze [Edo Tensei] and Naruto [Sage of Six Paths] are the most popular ninjas that are being used these days. The Fire element would be the next one, Uchiha Clan Ninjas are Fire Elements and last but not the least, Earth Element that gives a boost to Kakuzu [Earth Grudge Fear] users.