I have both and have used them extensively for work and play. I find Neoshell noticeably more breathable than eVent, which is impressive. Neoshell has a nicer "hand", is a little quieter I suppose, and has proven to be functionally waterproof thus far.
Neoshell dries a little faster, and usually that is more important to me than straight up impermeability from exterior water. If you're out in gnarly wetness for a few days, you will get wet in eVent or Neoshell. I want gear that functions well when wet, dries quickly, and is water resistant enough to keep my dry for the first 12-24 hours of precip. That combo will get you through most trips in the Rockies very efficiently. Coastal trips are another story. I've never been wetter than approaching via bushes and then bivying in the rain for three days on Mt. Shuksan.
Good DWR upkeep and cleanliness is important with both for sure.
