Without hesitation, Snap On every time mate.
Your normal run of the mill gun will not loosen really tight wheel nuts and after two wheel changes the battery will be flat.
I use Snap On in the workshop and at trackside and the battery will last all day and will do about 30 changes (120 wheels) before the battery gets tired.
Downside is they are £400 - £500, however IMHO they are worth every penny.
Alex.