I use a mixed grip. Right over and left under. I have short, stubby fingers - like my pecker. I've messed around with a hook grip but I can't even get my fingers around my thumbs on a DL bar...
If you can hook grip then do it!
I have a teammate who pulled 870 in a meet and locked out 900 only to pass out and he's hook grip with not a single dropped lift.
I have thumbs like spark plugs so I have to alternate grip.