If going to Galveston, Med Center, Southern Burbs, Fort Bend, Pasadena, or NASA....Hobby.
If going anywhere else...IAH including Downtown

IAH usually has shorter security lines. Remember you can access Terminal A via the other terminals either pre or post security.

IAH has better food services and club options

IAH has more flights on any airline except WN and Jet Blue. So in a IRROPs situation youre better off at IAH.

IAH has easier rental car and parking choices.