Current Champion: Brock Lesnar
Next Champion: Jon Jones, some guy when Brock Lesnar retires
For those of you who try to hate on Brock Lesnar, you better get used to it. He is becoming exponentially better (approximately an increase of his skill multiplied by itself, every fight) and has everything.
He has a decent stand-up game with which he defeated Couture with. He has an unstoppable wrestling game, which he used to stop, well, everyone. He is picking up a submission game with a Purple Belt in Brazilian Jiu-Jitsu, which he used against Shane Carwin.
Most would say that he just laid on him, but was pure Jiu-Jitsu. He noticed the opening, and Carwin's struggle to get his breath under control.
From there, he proceeded to move into side control on Carwin's left side. He locked in the arm triangle, and squeezed. Fight over. Yes, it was easier than many submissions, but to say it was not skill, is to admit your lack of knowledge of the sport.
Jones is an amazing fighter, but if, or when he moves to Heavyweight, no one will be able to have the advantage against Brock in just about any way. I say Jones moves up two or three years from now. By then, Lesnar will have picked up excellent boxing, and a likely Black Belt in Jiu-Jitsu.
With all of that, plus his unstoppable wrestling and takedowns (I believe the all time record holder for takedown percentage), and he will be literally the most unstoppable fighter to ever step into a ring.
Some think he can't get through Cain Velasquez, and possibly even Junior Dos Santos, but I feel it's only a matter of time.
Cain is a medium-sized heavyweight, and his wrestling is most likely not as good as Brock Lesnar's. Clear advantage.
I also doubt that Junior Dos Santos will be able to stop Brock's takedowns, and he won't be able to knock him out. If Carwin couldn't, "Cigano" can't.
Also, I must reiterate, do not just comment on Cain/Lesnar. Please take into your mind everything I say about the matchups and the entire article.