Depends on your preference - I really like 6MOA dots - to me it's becoming a requirement increasingly.
The best: Trijicon RMR 6.5MOA
Good: Sig Rome1Pro 6 MOA, Trijicon SRO 5MOA (great to shoot - not quite as robust as the RMR - I have 2 SROs - love em - just not as much for carry)
Good but...