The cheapest rates are going to have shorter contract terms. For instance, a 3 month term is cheaper than a 6 month term and a 6 month term is cheaper than a 12-14 month term. So if you are able to remember to call before your contract expires (they will notify via mail you that your contract is about to expire), then the 3 or 6-month term is your best bet. If you don't call to renew/cancel, you will be charged a much higher variable rate on a month-to-month basis. If this is you, sign for a 12-month contract term with the cheapest rate.
Another unwelcome side effect of not knowing your average monthly kWh usage level is that you may end up paying more than you expect. This can occur when a customer inadvertently shops an electric rate based on a higher usage level than they actually use. Electricity suppliers commonly advertise their electric rates associated with the highest (2000 kWh) usage levels since those tend to be the lowest rates.
After spending so much time and energy with energy companies, I figure I should pass this info onto the internet world (within Houston). I am a Centerpoint Energy resident (you don't get to choose the electricity provider you have; it's based on where the electricity is provided). I think Houston is predominantly a Centerpoint energy area (correct me if I'm wrong).
There are a variety of different types of gas and electricity plan that are currently out there for prospective customers to consider. Some plans offer fixed rate deals , these allow you to be sheltered from price rises over an agreed period of time. Other plans allow you to manage your entire account online, making it easier and more efficient for you to handle your energy supply.