To fix or not to fix...?
There will be a few exceptions, however, for some very low or very high consumers of household energy. It's worth checking to see if either of those covers your case, but staying on a capped rate is still the safest option for almost everyone, for now.
See https://www.moneysavingexpert.com/latesttip/?anchor=energy&utm_source=MSE_Newsletter&utm_medium=email&utm_term=04-Jan-22-601f0e1500346a58738-61d4bc53452a53e583486e234472563f&source=CRM-MSETIP-601f0e1500346a58738&utm_campaign=nt-hiya&utm_content=3#energy