As mentioned by Shleepy they are totally different headphones, however the Sennheiser's are definitely my pick. For one, the E2Cs are sort of a bottom of barrel model by shure whereas, the HD280s are a very fine sealed circumaural by Sennheiser. The isolation with the HD280s, while not quite an in ear monitor, is still probably the best of any full sized headphone. With regard to comfort the 280s are probably a little more comfortable unless you have a very big head. With regards to portability the shures win hands down.
But theres a reason why the Sennheiser HD280s are a standard in the audio industry, theyre a really good deal.......If you look harder you may even find them for 100 bucks or less.