So far we are very happy using Frontier Utilities!
We've been using Frontier for about 1.5 months, so our experience is a bit limited. That being said, it's been positive so far. The portal is easy to use, and we receive timely notification of bills, updates, usage. etc. Additionally, they have been responsive and proactive with communications concerning the wild winter weather, folks without power for multiple days, and information regarding billing.
The first bill was less than $5.00 and I couldn't pay on line and could not get anyone to talk to me on what was needed. Two emails did get me an agent that worked out the payment with me. I'm not sure that it has been settled.