Overeem and Anderson are the two best as far as straight up skill goes, imo, but Silva has the chin and that weaving that keeps him unfazed and allows him to be more secure.
Pettis is next, Aldo closely behind him (I had Aldo above Silva a few years ago, but Anderson's boxing has improved since then).
Then it's Barboza, Alves, Daley, Hunt, JDS and Njokuani to fill my top 10, and after watching Conor McGregor's past fights, he's close to the highest level, just needs more good comp (which can change things). Order:
1. Overeem
2. Anderson
3. Pettis
4. Aldo
5. Barboza
6. Njokuani
7. Hunt (is tough to place, could be higher or lower. Is good at pacing himself, but his age combined with his weight limits him more than before)
8. Alves
9. JDS
10. Daley
Barboza was headed to K-1, Njokuani is on his level, Hunt and Reem won it, and the rest with the exception of Alves and Daley would be near the top there. Mousasi is on the level of Alves and Daley, he's one of the best. As is Gus. Gus & Mousasi are the best strikers at LHW.