The
Power To Choose site, posted by kootr, is absolutely the best resource available to help Texas consumers select a power provider.
I'm surprised, though, that your apartment complex offers a choice. That's the exception, rather than the norm.
When all is said and done, it's not much different from picking a cable, internet, or cellphone provider. Take advantage of any specials, be sure you read the fine print associated with them, and don't sign up for anything that'll lock you in for too long because you want to keep flexibility to change providers should you see a better deal from another one.
The one HUGE difference is that the power itself is all delivered and maintained by the same electric company, no matter which middleman you go with. So there's no more or less reliability to worry about. It's all about the rates, contracts, billing arrangments, and about how they treat you when you call them.