I’ve just spent ages looking. Started on a low budget just to record where I’ve been and ended ordering the Edge 800 with Performance and Map bundles.
What I got from looking around and speaking to people who use them is that once you start using it you will use it a lot. That made me decide to get the best one I could afford and keep it for a long time.
As I understand it the GPS chips in the new Edge units were replaced fairly recently with newer ones which pick up a signal better. That and a warranty made me want to most recent one available too.
In the Edge series the 605 is the first one with maps you can view out and about.
Guy I know bought a Bryton from Wiggle and seemed fairly impressed – it was the first time he’d had it out so not long term enough for a proper review.