Basically there are 4 categories I'm sure you looked at:
1) Actual price per kilowatt: Self-explanatory
2) Rate type: Fixed or variable. If it's variable, then you could pay more during more demand and less during less demand. This matters more if you're gonna crank the A/C on all the time, you'll probably want fixed, otherwise it really doesn't matter, I think.
3) Renewable energy content: Also self-explanatory
4) Contract term + termination fee: How long your contract is for, and how much you pay to back out of it.
To be honest, only 1 & 4 truly matter. I wouldn't go pick a company that requires a 3-year contract if you might have to move out of your place (unless you can transfer it, but I don't know that. And renewable energy content is just to make yourself feel good that you're not killing the planet.
See, so simple!