As of this weekend, I've now used both. I was also a bit concerned about the lack of pit zips in the Vapor Stormlight jacket, but they jacket overall is lighter and breathes better than the Chugach. I hiked for about 10 hours on Sunday in the rain, snow, hail wearing the Vapor Stormlight and could not be happier with the waterproofness and breathability. I stayed dry from head to toe. The finish on the Vapor is also a bit quieter than the Chugach and the jacket "moves" with you better. The Chugach is thicker, and therefor probably has the edge on durability in the long run or for all day every day use or busting lots of brush.
I have not used the KUIU Ultra NX rain jacket, but feel that is probaby a more fair comparison to the Vapor Stormlight. These are ultralight, packable jackets to bring out when the weather turns south. I have not got my hands on it yet, but the new SEAK jacket from FL is probably closer to the Chugach.
So the real question is what conditions will you be using rain jacket for?