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.
If you live in the greater Houston area, there are over 60 different energy suppliers competing for your business. Many of these providers have websites that are confusing and difficult to navigate, their rates buried in misleading advertising and dense jargon. Who has the time to sort through and keep track of options across all these different sites?