I prefer the E175, which feels more spacious to me. Both aircraft are very safe.

I assume the BGM-ORD/MDW leg is a mainline aircraft, but you know that on the leg with the CRJ/E175 you will likely have to gate check any luggage larger than a large laptop bag, so be sure to take out anything you will need onboard before boarding.

Ditto the advice to check seatexpert.com and try to select a good seat far in advance - beware that bulkhead seats on the CRJ do not necessarily have more legroom.