Usher is incredible at adapting to all kinds of styles and trends but I think his chameleonic tendencies mean I see his music as only being as good as how into a current trend I am as a listener. He brings a sense of purpose and craft to EDM-by-numbers stuff but I still don't want to hear something "DJ Got Us Fallin' In Love" because it's otherwise rubbish.
I like Miguel as a personality a lot. I find a lot of male r&b singers come across as being sleazy in their overt sexuality, or unconvincing if they're unwilling to commit, but he manages to straddle the boundary between lascivious and endearing. He has a softness, basically.
Jeremih is good as well, his gossamer voice means he can sing some really nasty stuff and it still sounds sweet rather than predatory and discomforting.