Not sure if you have a class date yet but if you have a choice I would try and get the 175. That would mean a commute to IAH and you would not be going going between AA hubs and thus not fighting a ton of employees traveling non rev. But that also means you couldn't get back to PHX until you upgrade and then holding PHX as a CA is a very long wait. IAD commute is going to be a 2 leg commute most of the time since United only operates one direct flight a day. If I had to choose, I would go for DFW on the CRJ if you can't get the 175.