It appears the 700s will slowly goto PSA in 2017-2018. Envoy will have over 100 ejets over the next few years, and close to 100 145s until 2022-2024ish.
You should pick what is best for you long term. Both are in good positions for long term sustainability. Envoy does appear to be contracting some in ord.
I'd highly recommend taking an airline with flow. I have a few friends who are captains at skywest and can't get a call from the majors (why I have no idea) and can't afford going to a lcc. Tifiw