I've been using Panda for over a year. Just signed up for another contract as the discounted rate was still availble even though i was an existing customer. This wasn't the case with the (many) suppliers i've used in the past.
I usually go onto Bonkers.ie every year at the end of my contract, enter my annual usage for gas & electricity, and go with the cheapest. It only takes minutes. If you don't know your annual usage in kWh, ask your current provider.
I don't understand why everyone doesn't do this.