I have both the Tamron 17-50 and Rokinon 8mm for my T2I. I haven't had my setup that long, but the Tamron is a dope, sharp lens and a great deal. You can do follow cams and as well as get longer shots and good B-Roll/ lifestyles.
I really like the Rokinon 8mm as well, but it's really up to you if you want that fisheye look. As stated above it can look very much like a Gopro if you don't use good fisheye filming technique such as keep it low, find good angles, ect... It also doesn't seem as wide as the classic VX/HXV fisheye that you see in many skate/snowboard videos. I would def get it as a skate/snow/ski lens action lens, but it's not that awesome for other things like inside of buildings, tight spaces, ect... bc you get that weird barreled distortion.