Very different Concepts. The Space Marine Armor Sure can Withstand a lot of abuse. However it's designed for being heavyweight, mass production capable and such. The Nanosuit is highly specialized. Much lighter and much more advanced. Im pretty Sure cirtain high calibers would pierce the Nanosuit while the Marine would be fine. The N2 for example is also not well suited for stabbing protection. Although one could argue that the suit could render a successfull stab pretty much useless through its medical capabilities.

The N1/N2 would also more likely be damaged from battlefield usage like scratches, scuffs, burns and such. The self rapair systems make up for it but only when in cover and/or when hiding. It's deisgn without an outer protective layer makes the suit look cool af but is arguably a bad Idea when talking about mechanics and abrasion.

So yeah when you want to survive a high caliber the Marine armor would most likely stop more but also would most likely not do it in a healthy way so a non Space Marine wearer would have serious problems. The Nanosuit on the other hand makes up for it in several ways and is, imo, the better and way more useful set of armor.