I personally try to use my forearms as little as possible when doing biceps. Why let the forearms do some of the work when you're trying to get bigger biceps? And screw concentration curls, preacher curls and all the other crap. If you are wanting mass, just stick to barbell curls or ez bar curls. As heavy as you can go for 6-12 reps. I find the barbell works my biceps a lot more but will hurt my wrists some times. Oh, and any time you do a curl make, sure your hand is away from you, not towards you. Make sense? If you have your hands pointed in front of you at the top of the curl instead of pointing to the ceiling, you will feel it in your biceps much more. This makes it so you can't really rest at the top. Don't be scared of big weight. I'm still not up there with the big boys, but I can barbell curl 155lbs for 6 reps or so.