Petrosyan is the best overall kickboxer at the moment. I dont follow very many guys that fight full rules MT, but as for guys that have the essential thai style, Id go with Buakaw, Bonjasky, and Yod Fairtex when he was in his prime (even though he has started to decline, he is still a beast). Another guy that doesnt get mentioned among the greats a lot but is a complete beast is Nathan "Carnage" Corbett. If you have never seen his fights, then go look some up on youtube. Some of the best elbows and body shots in kickboxing. The guy is an animal.