Incredible striking. The best in all of MMA for sure.
The thing with Overeem's development is the fact that he has been showing alot of improved solid defense and timing nowadays, instead of just brute strength.
The scary thing with Alistair is, he has crazy strength and size, with the gas tank to boot, and his technique is almost perfect. He is one scary fighter, especially in MMA, because he is easily the greatest striker in all of MMA (please, spare me the "Anderson Silva is the best"-nonsense), with very good ground game, and a killer guillotine that is every wrestler's nightmare, and a rock solid gas tank.
I'd pick Overeem against any MMA-fighter today, other than Fedor, to be honest.
He would merk Brock in 2 minutes.
JDS has shown good offensive boxing but seems to lack the defense to handle a striker of Alistair's calibre, so he would most likely get smoked as well.
I have a feeling 2010 and 2011 is going to be amazing years for Alistair. Can't wait for Dec. 2nd, the K1 finals is going to be siiick