The optimal if using Enmax is to get on the RRO rate for electricity because you can see its rate at the start of a month from
http://www.auc.ab.ca/Pages/current-rates-electric.aspx. Then for that month, just select whichever of RRO or fixed is less using your online account. ATCO has lower admin fees but doesn't do RRO in Calgary so you're more exposed with floating rates.
The floating rate for natural gas has been much cheaper pretty much since fracking became big.