NARS blushes are definitely highly pigmented. well, most are. For me that isn't always a good thing because it's easy to overapply. A stippling brush like the 187 is a godsend because it picks up very little color.
I started out with NARS blushes, then switched to MAC and i've had absolutely no issues with the MAC ones. I like the fact that MAC separates the different finishes (satin, sheertone, frost,etc). I particularly like the sheertones, because they're matte and very silky.
I can't say I prefer one or the other. There are some shades I really like from NARS, and some unique MAC shades that I can't live without. For example - i haven't found a MAC dupe for NARS Albatross yet. and vice versa- I haven't found a NARS dupe for my Pinch O Peach. The pinky NARS blushes are far too bright/cool shade for my liking.
MAC blushes are slightly bigger and cheaper as well. So I'd say for sheer value alone I'd choose MAC.. but definitely check out NARS blushes, there are some gorgeous standout shades