Overall history, the teams are pretty similar. The Astros won a pennant in 2005, and the Rangers in 2010 and 2011 I believe.
I'm personally an Astros fan, and don't see that changing. I grew up a big fan of both, going to several games every year in Arlington and one or two a year for the Astros. It was always awesome in Arlington (and probably Houston too, but I went to games with different people) because regardless how cheap the tickets we bought were, we were going to end up with front and center seats because no one was there. This is my biased and impressionable perspective, of course.
What turned me off to the Rangers was as soon as they saw some success all these fans showed up on social media that I'd never seen. All of a sudden they were propping themselves as Texas' team, similar to a university in Austin.
The fans of the Astros I've seen have been there through thick and thin, and there has been some quite thin this decade. Yet despite the terrible product, fans were still there in the top 1/3 of the MLB (corrected from mistakenly typing 1-3 instead).
Another thing that rubbed me wrong was they hype of A-Rod and how quickly they turned on him when things went south. The trade to Bronx and steroid suspicion came shortly thereafter.
The best Astros that I recall seeing playing, the Biggio, Bagwell, Berkman, Oswald, and the above average players like Shane Reynolds started their ML career in Houston and stuck around for most of it. I've never been a big fan of the pay a guy huge to be a mercenary (to which the Astros of the 2000s have done as well, of course, part of their late 2000s struggles), but generally I feel like the Astros have done a good job most of the time.