|L-R Glow, Matte (both Mont Blanc)|
Having now used both, I thought I would do a little comparison post!
The packaging is pretty much the same for both - the iconic matte black that Nars use with bold lettering - although Sheer Matte has a frosted glass bottle so you can distinguish between the two.
I can't say if this applies to all the shades in the range, but Mont Blanc is very similar for both foundations with Sheer Matte pulling ever so slightly more yellow in tone, whereas Sheer Glow is what I would call a 'perfect neutral'.
Application & Coverage
The consistency of these two is very similar (not too thick, but liquid enough to blend easily), and both foundations provide a similar amount of coverage; although I would say that Sheer Glow blends just a tiny bit easier.
Quite obviously, Sheer Matte has a much more matte finish that Sheer Glow, but I find on my skin at least that Sheer Glow isn't massively dewy but just a nice natural texture. For summer, I would recommend Sheer Matte more, purely for the fact that you would need to powder a lot less.
Both of these have some great staying power. I can get a good 5-6 hours wear, and longer if using a makeup setting spray. Having said that, I do find my face gets shiny faster with the Sheer Glow if I'm on a night out and dancing a lot.
Overall, it's going to be down to personal preference as to which you think is better. For the moment, that's Sheer Matte for me but I might revise this when it gets to the colder months and I inevitably have drier skin!