Jobs: HA! My husband, a native-born U.S. citizen, is fully bilingual (unaccented English and Castilian Spanish), has an MBA from a major university, almost 2 decades of experience in hi-tech and petrochemical industries, and has not been able to get even a call-back in 3 years of applying to jobs all over Texas. He has spent nearly half of our 30 months in TX unemployed, and the rest underemployed in jobs he hates. Good luck, you'll need it.
Weather: No real difference.
Terrain: Sugar Land is FLAT. Round Rock is in the Hill Country. Both suffer from urban blight. Right now, Sugar Land is inundated with construction along Hwy 6.
Weather: both locales famous for triple-digit heat and humidity in the summer. You'll feel right at home in either, but Sugar Land is much closer to the Gulf.
Home Affordability: Cost? Varies widely. You can get a NICE pre-fab house on a good piece of land for under $100,000 or you can easily pay millions. Taxes? Try another state! Taxes are obscene here.
Crime: Sugar Land is a Houston suburb. Since the onslaught of what the locals call "Katrina debris," violent crime rates in the Houston area have had the greatest increase in the country (13% increase in 2006--stat just released today). Round Rock is an Austin suburb. Not crime-free, but not making national news for crime rates, either.
Nightlife: 6th Street in Austin has 'em ALL beat, but is not family-friendly (Austin is a college town). Sugar Land (and Houston in general) is much more family-friendly. Both, though, are within a reasonable driving distance to a Schlitterbahn water park. The original in New Braunfels (closer to Round Rock) has been rated the best water park in the country (and rightfully so) for several years consecutively. Sugar Land is fairly close to the new year-round indoor Schlitterbahn in Galveston. Haven't been there yet, but folks say it's pretty cool.
Education: it's a crapshoot. I teach in a Texas public school, and, quite frankly, things have no chance of improving until they scrap the TAKS test. The Texas Education Agency website has info for comparing school systems based on numbers, but no way to note the intangibles (crime, drugs, attitudes of students/staff/community) that make all the difference. The school I teach in has a student body with "a bad reputation," but is a much better environment than the "good school" in a neighboring district my son used to attend, but in which my son was bullied so much (without consequences for the offenders) that he couldn't study. Do A LOT of homework here, including frequent visits, and keep your options open (private school, homeschool, etc.)
All things said, although I didn't live in Texas until I was 40, I wouldn't dream of living anywhere else. GOD BLESS TEXAS!