The difference between using 10w30 and 10w40 should not cause any change in how the engine runs. The best oil to use might be whatever is printed on the top of the oil filler cap on the top of the valve cover. Here is a URL that will tell a lot more about motor oil than you ever imagined there was to know:
http://www.bobistheoilguy.com/
I think any oil you buy (other than used drain oil) would be fine for your car - but the later model cars often call for 5w30. If you live in Houston, I dont think it ever gets cold enough that 10W30 wouldnt be equally good. An important point is to change it often enough. You can read about that at 'obistheoilguy'.