Eminem is my GOAT but that's too easy, my taste in rap music gets weird after that.
Tech N9ne is my #2, nas 3, and I am utterly obsessed with both wu tang and bone thugs. I think the best rappers in wu tang are the most slept on, inspektah deck and rza were the reason that 36 chambers was such an epic classic, they bodied every verse in spectacular fashion. Krayzie bones gift for blending speed rapping that actually makes sense and melody is one of a kind. Los(lesser known Baltimore rapper) is a lyrical god and one of the greatest wordplay rappers I've ever heard. lil dicky is probably the best blend of lyrical genius and general appeal out there right now, he's too hilarious and likeable to fail but he will shit on nearly any modern rapper bar for bar.
Kid cudi isn't a rapper but somehow falls in this genre, imo he is a genius musician with an untouchable gift for melody that can't be practiced or taught, and a gift of reaching people on a personal level, his production puts you in a trance, his weird ass groan-singing is so catchy to certain ears and really grabs you, and he has shown an ability to rip a verse apart with raw lyricism but it's not his strong suit.