Kinda bold move here. While several other US carriers are scooping up E170s as fast as they can (US, UA, DL), CO goes for the contrarian move.
I've heard great things about the Q400 - near-jet speed, comfortable, quiet, very fuel efficient. I haven't heard anything about the ATR 72-500. Is it comparable to the Q400? Is anybody still flying the ATR 72 in the US? Unfortunately, I still think about the AE crash in Indiana when I hear ATR. Did they re-design the wing to deal with the icing issue?
If CO buys either of these aircraft, they will have to launch a marketing push to promote the positive features of these aircraft (roomy, quiet, possible 2-class service[?]) to overcome the anti-turboprop attitude that still exists. CO made point of hyping its express fleet when it went all-jet. It will have to make just as much noise about the wonders of its next-generation turbos for this move to work.