To confuse you even more... all those three PSUs; Corsair, XFX and Antec (recommended by obsidian86 are manufactured by Seasonic.
Antec has been a long time Seasonic customer, Corsair got into the PSU business about 4 years ago I think and XFX is new to the game.
I know the Corsair HX620 has gotten really good reviews over the years. I haven't read a review on the XFX P1-650X-CAH9 650W, but since it is built by Seasonic I feel comfortable with a "blind" recommendation for it.
Antec PSUs used to be really good in the past, but they seem to have cut corners here and there when they ask Seasonic to design PSUs for them (based on some past issues I've read regarding long term reliability). I consider Antec PSUs as "merely good" instead of excellent which they once were a long time ago.
Overall, my recommendation is Corsair due to the 620HX's history.