I love Mufe Mist and Fix. I only use Mac's fix+ for pigments, but mufe on my face. Mufe has never irritated my skin, but fix+ bothers some people. Mist and fix keeps my make up on all day w/o transfer and has zero smell. I think mostly it comes down to whether or not you are irritated by Mac face products and just brand preference.
I use both of these products almost exactly the same way! I use Fix+ before my foundation and to wet my brush for foiled looks/working with pigments, while I use the MUFE Mist & Fix to set my makeup before a long day/night out. I find that I use more of the Fix+ (I've been through several bottles) because I also like to use it to freshen up my makeup during the summer in the heat, but the MUFE is awesome for finishing your makeup and having it stay in place.I also prefer the Mist & Fix. Despite its name, I don't find Fix+ to be a TRUE fixer. I actually use Fix+ BEFORE I apply foundation (I'll spray it on my face, or on my brush before I blend my foundation) and I use Mist & Fix AFTER I apply my finishing powder. I just find Mist & Fix really does a way better job at actually setting my makeup and making it last all day long.