I would be wary of many reviews and consumer groups… many web site consumer review sites I wouldn’t touch with a barge pole.
The Ofcom report is the only review I would trust for fixed line, mobile and broadband… and there is differentiation or parity on key categories between providers and also trends so I don’t think really that tricky at all. You choose what is important to you, cross check with the Ofcom report and if available in your location and at the right price point for the service levels you want then consider subscribing.
From a ‘speed’ perspective, those that use the Openreach network are going to be reasonably consistent, although on superfast if you are at the main transition curve distance from the street cabinet, you could see a fair amount of variation between ISPs… due to the settings they use to optimise the modems on their routers, and different ISPs may suffer from different amounts of congestion on the backhaul. Virgin for example has suffered in the past with this.
I would check for reliability and customer service.