More often than not, your old supplier will offer you a better deal to try and stop you from switching. Fair enough. But before going ahead with the switch, make sure you have compared the quote correctly. 

What are the unit rates and standing charge comparatively? Is it genuinely fixed or can prices fluctuate? Squeaky offers a fixed year tariff for 1 or 2 years and locks in prices for the duration of your contract. Make sure you read the T&Cs and know when the contract ends so you're not at risk of going into out of contract rates.