David Tao is my choice. The definitive of a R&B pioneer in Chinese music scene. Alex To did have R&B elements in his music earlier than David, but to me, he is more like a disco king hehe...
I much prefer LeeHom in his earlier days, with "Qing Di Bei Duo Fen", "Ru Guo Ni Ting Jian Zhen Shou Ge", etc...But then, his music was not recognised until around the "Gong Zhuan Zhi Zhuan" album. That is when he started to become commercialised... sigh..
Jay Chou is not totally R&B, but he is pretty talented. Though I admit I can't understand a single word he mumbles unless I look at the lyrics hehe. But again, who can mumble like he does?

Harlem is not R&B, and again, I much prefer his older songs like "Rang Wo Yi Ci Ai Ge Gou" and "Gai Bian Suo You De Cuo". His popularity dipped after that though, and he switched to hosting, and occasionally releasing songs like "Kao Jing", "Qing Kai Chuang" which were not bad, but did not make him really popular until "Qing Fei De Yi". Before the song, his nomination in awards were always the "supporting role" - good enough to be nominated, but yet not good enough for the award that kind. So the Best Male award is sort of long overdue, I guess..