10.5K AA miles x 5 pax (Status: EXP)
AA CLE-ORD 8:13PM-8:55PM RJ145
AA ORD-MCI 10:10PM-11:42PM A320
Pros: Shorter travel time.
Cons: Riskier weather in the winter in ORD, RJ145 flight with no WiFi or E+, AA reliability.
10K UA miles x 5 pax (Status: GS)
UA CLE-IAH 6:35pm-8:50pm 737-700
UA IAH-MCI 9:35pm-11:35pm RJ175
Pros: GS protections, better planes
Cons: Long flight time, short connection
With AAs track record, I'd consider that a shorter connection, so unless you say IAH transfers aren't simple (never been) the connections are more or less even. Presumed delays makes the extra travel time with UA closer to an hour vs. 90 minutes. Since neither have another flight that night to protect you on, what the alternative would be should you miss your connection, should be compared as well.
If you can get the first 5 seats 1A, 1B, and all 3 Cs on the RJ145, it won't be that bad, 2 hours on a RJ175 is nothing to get excited for over an hour on a RJ145.