I've had many Garmins over the years, most of which weren't bad but there were various things I wasn't happy with and a while ago I had a good look around and found the SatMap Active 20. Not cheap if you go for the top of the line with the full O/S map set, but you do then get 10k/25k/50k of the whole UK (or you can just buy whichever maps you want separately). It auto-switches between maps as you zoom in and out, the scrolling/zooming is much faster than any Garmin I've ever had, and there's lots of customisation on route lines to suit you (colours/widths/opacity) unlike most Garmins (which was something that annoyed me). Also, while it has a touch screen, there are also physical buttons for everything, which I find much easier to hit than a touch screen while you're riding.
It supports GPS/Glonass/Galilieo and rarely loses lock, and it has a very good screen and the 5000maH battery lasts all day if you don't have the screen on full brightness all the time. The only real downside is that it's not the smallest or lightest of devices, but you do get the impression you could ride over it and you'd just bounce off, and they sell Quad quick-release bike mounts which make it a doddle to fit onto your bars.
Last I looked, they were selling some refurbished Active 20s, and a friend bought one which looked absolutely brand new, fully tested, with a warranty, and quite a bit cheaper than normal. You'd need to add whatever maps you want as the refurbished ones only come with the world basemap AFAIK, but it would still be a good amount cheaper.