I bought the Shure SE315 over the B&W C5 Series 2 that I had intended to order based on the Crutchfield rep's suggestion that the Shure's had better bass reflex. Not sure about that, but the SE315's do have very good bass reflex as well as excellent sound quality in every other aspect....if....
Great sound quality when proper seal is achieved; Well built, detachable/replacable cable; Many tip options provided
More of a process to put in and take out than many others; Near total isolation of outside sound in order to get optimum sound quality; Can be uncomfortable for long term use