I have a 14" .375 Win. barrel with a fixed 2x bushnell on it. I love it for the woods of PA. I personally prefer the 2x over a 4x, but if you are going to shoot in more open areas and are guaranteed a rest, I'd go with the 4x. All of my shots are reasonable close, and the 2x is really easy and fast to see through for moving shots.
I have a Burris 3-12x, but no Leupolds on the pistols so I can't really comment on the Leupolds (although I have several Leupold rifle scopes). Been very happy with the Burris, but also very happy with the Bushnell. Totally your choice...both brands have good track records.