You forgot Honey, arguably the most important song in KARA's history. I'm sure it's just an oversight right? The Japanese singles should be included also: Jet Coaster Love, Go Go Summer, Winter Magic, Speed Up and Girl's Power. Or maybe you could split the poll into Korean and Japanese releases.
This might overlap with 'most underrated song' but you could do a favorite 'filler' song. You know, those songs in albums and EP's but which never get released as singles or get an MV. With 3 Korean albums, 6 Korean EP's, and 2 Japanese albums KARA has dozens of songs that don't get noticed. This category would be a great way to give some love to those songs and see which KH members know their stuff.
Another category I think would be fun is favorite soundtrack song. KARA did a handful of those in their early years and several of the members have done solo/duets for various dramas.