Gexa worked for me
In Houston, I compared their price vs. Reliant Energy. Gexa's OnePass rate was ~10% lower. I signed up. I received the bonus miles on the last day of the period they quoted. (I think it was somehting like "8 weeks after payment of the 2nd bill.") I have been receiving 2 miles / $1 about 3 weeks of every month after I pay.
I checked the site today, and now their rates are higher than Reliant. Maybe they changed up the offer since then, because I confirmed I'm paying the low rate.