It depends what playthough you are on. If it is the first one go with Rampage or Gun Lust. If you're on the second playthrough make sure to put plenty of skills into Brawn skill tree to help keep you alive.
I tried going down the Brawn tree and it didn't work after all. Now my Gunzerker is a level 50. I am currently using the build at the bottom. I was fortunate enough to get a level 50 Legendary Berserker class mod which adds +5 to Locked and Loaded, Quick Draw, Filled to the Brim, Hard to Kill, and Incite. I found the skill Down Not Out (you can Gunzerk while in Fight for Your Life) was more beneficial at staying alive than putting a bunch of skills in the Brawn tree.
I also use two level 50 Infinity pistols so the I'm Your Huckleberry (Increased pistol damage) and Divergent Likeness (increased damage if Gunzerking with the same weapon type). I only put 3 points into the Brawn skill tree (2 in Hard to Kill and 1 in Incite) which when combined with the Legerndary Berserker class mod makes it 7 in Hard to Kill and 6 in Incite.
So as it turned out putting a bunch of points into the Brawn tree didn't work out to well. When I originally made the post I was level 39 and it was working well up to that point, but later oh man I was going down quickly which made me change my build.
http://www.bl2skills.com/gunzerker.html#145050001001415510512121000000000 --- When I'm concentrating, I never have more than one drink before dinner, but I do like that one to be large and very strong and very cold and very well-made.