APS was my provider when I first moved to Arizona from Washington DC in 2003. The fact that power remained on during and after storms gave it a huge plus after the horrors of PEPCO. The couple of times we did lose power during monsoon season it was restored within a couple of hours so no harm done. The service itself was reliable.
But--it was crazy expensive. We rented a two-BR apartment and the bills were over $100/month almost every month, including the cool season. Now some of this is because the apartment complex didn't maintain their HVACs (we lost power over July 4 weekend!) but it should have been much lower during the months when we didn't need AC or heat.
Since those days, I bought a home in SRP territory. More power failures but none last long and the cost is far lower in my 2-story townhome.
Disclaimer: I briefly worked on a contract with APS. They are phasing out storefront payment in some areas. You can pay online with a credit card but there is a fee charged by the third-party processor (can't avoid this). The best way to pay is to set up automatic payments online. Also check their site for tips on saving energy.