I’ve used both! Glossier is more of a moisturizer that also primes the skin and the smashbox is more of a primer that also moisturizes the skin. Glossier is thick and white and smashbox is lightweight and more ‘serum’ like if that makes sense. If you have very dry skin and only want one product I’d probably pick the glossier. If you have normal to combination the primeriser might be sufficient on its own. I use the primeriser on top of a hydrating serum - my skin is normal to dry with occasional breakouts.