User blog comment:Sean34/heavy bow gun/@comment-98.217.100.40-20121001101432

Honestly it depends what you intend to do with the gun for the most part. I only play MH3 so I'm going to answer this question from a MH3 point of view.

Some good gunner abilities are:

Critical Eye+3, Reload Speed+1/2, Recoil+1/2/3, Load Up, Bomb Boost, Trapmaster, Normal S Boost/ All Up, Pierce S Boost/All Up, Pellet S Boost/All Up, Crag All Up, Clust All Up, Bonus Shot, Status Atk Up, Elemental Attack Up, and Attack Up S/M/L.

Those are just some, but like I said it's up to what you want to with the gun. Example. If you want to use Elemental Shots to hit monster hard you would probably want EAU, Load Up, and AUS/M/L.