This is a tough call, he's definitely up there but I would argue that there are more than the obvious. For example, guys like GSP aren't knockout artists but uses his strikes incredibly well to set up other things. Hunt might not be technically crisp but his power is absurd. Overeem has better striking credentials than Anderson, Ado and Pettis combined, granted the Bigfoot fight makes people think he's a washed up nobody now but that is the reality of it.
For me:
(in the UFC only)
01.) Alistair Overeem
02.) Anderson Silva
03.) Jose Aldo
04.) Junior Dos Santos
05.) Anthony Pettis
06.) Jon Jones
07.) Renan Barao
08.) Georges St-Pierre
09.) Mark Hunt
10.) Vitor Belfort
UMMMMMMM. The Alistair hype has gone to your head in a bad way. This list is all sorts of weird. GSP better striking than Belfort?? AND Machida? Hell even Erik Silva or Edson Barboza