Other than at major morning (6:00 to 9:00) or evening (4:00 to 7:00) rush hour times, you're just as well off to stay on I-10 right through the heart of Houston. This also saves you from having to catch an exit. Just get in a 'middle-ish' lane and keep up with traffic - and keep an eye out for major interchanges. I wouldn't even bother with the in-town loop, I-610. If, on the other hand you want to transit the city during one of the rush hours, then, I'd probably use Loop-8 to the north. Although most maps show it as just another surface street in the northeast corner of the city, I have driven it and it is Parkway quality with just a few intersections with traffic signals. I would not try to use either US-90 or Alt-US-90 out of the city, but rather stick to I-10 until you are well clear of the suburbs at which point there will be many opportunities to get off and use US-90 which runs parallel to I-10 all the way to San Antonio.

AZBuck