1 - which airport are you closer to? This may be a big factor that could you cost you a lot of time every week
2 - If you want upgrades you won't get them on Southwest since they don't have first class.
3- If you are closer to Ohare you can choose between American and United. I'd say that decision is probably a toss-up. You could call both and try to get a status challenge - that may make your decision for you.