https://energyswitchma.gov/#/

I just pick the lowest-cost 100% renewable option that doesn't have a cancellation fee. If you don't care about 100% renewable, your cost would likely be lower. Keep track of when the contract runs out (I set a reminder in my phone). Before the contract ends, or earlier if I think of it, I go back to the site and see what the current lowest rate is, and sign up with that supplier.