I have owned the original Monster Turbines, the Golds, and the Coppers, I am currently using the Shure SE215. I think the SE215 are better than the original MT's and very close to as good as the MTPG while definitely not as good as the MTPC. The SE215 does have a better sound stage than all 3 in my opinion, the bass is while not as heavy is of better quality than the original MT's and almost as a good a quality as the MTPG/C but again has slightly less quantity. The midrange is better than all 3 of the Monster's and is more forward than all 3. The treble is better than the MT, as good as the MTPG, and not as good as the MTPC. The SE215 is more comfortable and less microphonic than all the Monster's and is easier to fit to the right depth to achieve optimal sound. Build quality is a bit of a toss up as the MT's are all made of metal so by default should be better constructed but they also have had known QC issues where the two metal halves are joined. The SE215 on the other hand is new so is not time tested and I have seen a few posts where people have had driver issues. The original MT's do not have the lifetime warranty the MTPG/MTPC have though and the lifetime warranty is not transferable so is negated if you buy used. Otherwise they both offer good warranties.
Long story short I recommend the SE215 especially if can buy the from a B&M store that has a return policy (Bestbuy??).