Welcome to FT! I am another IL Flyer, mostly out of ORD, but will try to fly out of MKE to maximze EQMs (if it makes sense and if the times work - sometimes, I take the easy way out and just fly out of ORD).

Pinniped has great advice!!!!

I am a UA flyer and for the most part, as a lower level Elite have been pleased. The E+ was my major deciding factor in selecting a program to be loyal to over AA. I have been able to redeem awards for very cheap with minimal miles (ORD-HKG for 65K and $50 in taxes, 12.5K 1 way saver awards, saver awards to Vegas for my parents). Once I hit the 1P level, I have been very lucky on UDUs (and enjoyed the occasional UDU as a 2P). I do like the fact that you can create a OP account and link them and have matching status on CO. I matched to a Plat and have enjoyed EUAs (CO verison of UDUs) on every 2-class cabin flight that I have flown on CO.

In my opinion, the Star Alliance network has more options for redeeming miles internationally, and that is what I tend to look at for redemption. If you are flying long haul international flights, UA has E+ which is welcome on long flights, AC is very good internationally and LH is not bad either.

I am in a wait and see mode in regards to the other changes to the MP/OP program. If you read the UA boards, you will see some of the changes that are not very popular now. I may consider changing to AA at some point, but I am not running (yet) to make the switch.

The good thing about Chicago is that we have options for airlines.