Can you go to the stores to try on the bags? If you can, you should go and see what really grabs you, and get that.
Also, it really depends on what you want to use them for. I have both MJ and MbMJ but I end up using the MbMJ tons more because it's my school bag and I can throw it around.
I have two MJ but, do not own any Marc by MJ's. I love mine but also like the other line as well. I think one of each would be nice..if the sale listed above is still available. Or purchase a MJ now that is on sale and wait until spring for a marc by MJ.
I say go for the bag you love. If you really want the MJ, then having 3 MBMJ won't satisfy you and you'll end up wanting to buy MJ anyways. On the other hand, if you like an MBMJ bag, go for it even though it's not "Designer line".