It is difficult to compare bags that aren't similar. To say that Coach or MK has smoother leather, for example, depends entirely on the bag. There are smooth Coach leathers and pebbled Coach leathers, likewise with MK, and each leather is designed to be different and feel different.
I have four MK bags and countless Coach bags, and I find the quality to be comparable. Both the textured and the soft lambskin MK bags I've had have held up very well to regular use, and I have very few complaints with my Coach bags, either. I've never had an occasion to test the CS at either store, as I've never had something break or need repair.
I have found greater variety of choices, though, both in design and as far as types of leather go with MK, though. Coach, while they change bags often, work within certain lines for quite a while and if you aren't fond of those lines then it doesn't leave much. Department stores, while they carry and feature a lot of the Hamiltons line, seem to have a greater variety of different styles of MK bags.