Personally, my favorite characters in Ouran high school host club are Kyouya, the Hitacchiin twins, and Haruhi(seeing as though I'm like a real-life Haruhi). I like the other characters,too. It's just that I like these most of all. Here's my list of my favorites (just the main characters)
1. Kyouya Ootori
2. Hikaru & Kaoru Hitacchiin(yes,they tie)
3. Haruhi Fujioka
4. Mitsukuni(hani) Haninozuka
5. Takashi (mori) Morinozuka
6. Tamaki Suoh
These are just my favorites. If you know the show or are getting to know it, you might have different feelings toward them. Feel free to create your own lists of favorite characters. I'll make a personality post next if that helps.
Oh! And here's a picture of Kyouya since he got left out last time: