I prefer DFW, but IAH is certainly easier than MIA - in my experinece the immigraion lines are shorter, the people more polite and re-entry to the secure area way nicer than security screening in the AA terminal in MIA. It's also easier to get around between the terminals, and the food is generally better.

I wouldn't, however, select IAH based on weather - Texas gets thunderstorms as well - the last time I arrived in IAH on BA 197 we held for a while about 30 minutes out from IAH, diverted to DFW where they discussed putting us on buses, eventually refueled, circled between College Station and Austin for 30-40 minutes and finally landed 3 1/2 hours late. It can be a similar story in DFW - I've lost count of the 3 hour weather delays I've suffered there; there are countless stories of aircraft being diverted to diverse places to Midland, Amarillo, Austin etc., and on extreme occasions parking for more than 5 hours before resuming the journey.