I would ASSUME due to the prices that the Shures are better. Sennheiser and Shure are both very good brands and on the classy/conservative side of things from what I've experienced. With a couple of exceptions, they seem to increase in quality with price in a predictable manner.
There are more experienced posters on this forum than me when it comes to headphones, but I have good experience with audio in general and I know this: The frequency range never tells the whole story. The distribution of sensitivity within that range, along with the acoustic environment its emitted into, is what dictates the "flavor" of the audio. A cheap headphone could have a massive frequency range and still sound like a tin can if all of the sensitivity is spiked in one area.
What kind of music do you usually listen to?
Do you prefer the heavy bass and sparkly treble of a "scooped mids" sound, or the detail and energy of a "pushed mids" sound?