I can ont say i have just one favorite, so will list some of them:
1. Kotomi Ichinose(Clannad)
2. Fuko Ibuki(Clannad)
3. Nagisa Furukawa(Clannad)
4. Tomoya Okasaki(Clannad)
5. Tsusaka Hiigari(Lucky Star)
6. Kagami Hiigari(Lucky Star)
7. Konata Izumi(Lucky Star)
8. Yui(Angel Beats)
9. Yuipee; Yuri(Angel Beats)
10. Kanade(Angel Beats)
11. Iwasawa(Angel Beats)
12. LeLouch(Code Geass: LeLouch of the Rebellion)
13. Karin Maaka(Chibi Vampire)
14. Negi Springfield(Negima?!: Magister Negi Magi)
15. Asuna Kagurazaka(Negima?!: Magister Negi Magi)
16. Madoka Kaname(Puella Magi Madoka Magica)
17. Kyoko(Puella Magi Madoka Magica)
18. Yui (K-on!)
19. Haruhi Suzumiya( The Melancholy of Haruhi Suzumiya)
20. Sun Seto(Seto no Hayanome;My Bride is a Mermaid)
21. Lunar Anamae(Seto no Hayanome;My Bride is a Mermaid)
22. Sakura(Cardcaptor Sakura)
23. Kyo Fujibiyashi(Clannad)
24. Kirito-forgot his real name-(Sword Art Online)
25. Yuuki Asuna(Sword Art Online)
Again these are just some of my favorite charcaters. Also, for the ones with no last name, I forgot their last name.