T.K.
I have Stream Energy and I am really happy with the rate, billing, and customer service. They are easy to deal with. Another one that is giving really low rates right now is Reliant. They were so high and lost all thier business, so, now they are trying to win people back with low rates.
It all comes down to how many cents per kilowatt they are going to charge you. One company may charge 12 cents and another 11 cents. The 11 cents is going to be drastically cheaper. The offer is usually connected to a fixed contract. So, they might offer 11c if you sign a 2yr contract or 12 c for a 1 yr contract. You can also choose green energy for a little higher premium. Here is a link that lets you compare rates and explains alot of what you need to know.
http://www.powertochoose.org/