A few things:
1. Do not wait until CO moves into the Star Alliance to switch as that will probably be when they stop matching elites on other Star Alliance airlines.
2. If you have relocated to IAH, I suggest you match to CO now and begin the year earning with them, assuming you can meet the qualifications for next year with CO within 10 months.
3. The main thing different about CO and UA in terms of their frequent flyer benefits would be with CO you have no upgrade instruments and instead have EUAs.
Overall I think you would be happy switching to CO now.