I have some of each - a couple of 4x, a couple of 6x, and several variables from 1.5-6 to 3-9. I did have a 4-12 for a while but didn't find much need for the extra magnification for my purposes.
A 4x would do for most of my hunting, but I do agree with erich on the advantages of a low-range variable on a drilling - I have a 1.5-6 on mine, which allows me to easily use the shotgun as a shotgun should be used, shooting birds and running game with both eyes open, looking through and ignoring the scope, while having that ability to wind up a bit for a longer shot with the rifle barrel.
Being able to wind on a bit more magnification also can come in handy on other rifles, especially on smaller game, if you have the time and the shot's a long one. For walking up pigs or deer though, I almost always either have a 4x or a variable set on the low end, and that does me fine. I also think a 4x is ideal on a .22 for rabbits.
