Well to be honest the characters I like are generally the sort of user that tend to be well let's just say tsundere. Now, I'm not that much big of a fan of the likes of Shana (Shakugan no Shana) , Louise (Zero no Tsukaima) , Nagi (Hayate the Combat Butler) and Taiga (Toradora) aka Rie Kugimiya's Four Tsundere Wonder's but I'm more of the line of a fan of the tsunderes like Rin Tohsaka (Fate Stay night) , Asuka Langley Soryu (Neon Gensis Evangelion, Adilicia Lenn Mathers (Rental Magica), Kyou (Clannad), Kagami (Lucky Star) all those have somewhat similar traits.
For guys, well they just have to be the cool and sarcastic type as well as the mental type. For example Accelerator (To Aru Majutsus no Index) is pretty damn badass while his counterpart the cool yet sarcastic dilinquent in Touma is also a good character, another good character would be Tomoya from Clannad and Edward Elric (Full Metal Alchemist)
Archer (Fate Stay Night) is another character I like as well as Arawn (Tear to Tiara) they tend to be pretty damn badass and cool.