My favorite male utaite, definitely. My favorite female utaite, however, is more difficult. I'd like to say ナノ (Nano), who's partly popular for her powerful, androgynous voice, partly for being very fluent in English (she's actually from New York and moved to Japan), and has since rocketed into anime music fame with original songs, plenty of singles and albums, and even a live concert. When you get the chance, here's her debut original.