Of those you mentioned, Britool were at the very top! They made a huge selection of tools and were pretty much unbeaten! Sadly, like many British firms, quality gradually declined from the late 70's, and the factory site is now a housing estate! You'll find the name around, but it is just a name, and the tools are imported.
King **** were always 'middle of the road'! If you needed a particular size of wrench or socket, and popped out to get one, it would more than likely be King **** you'd find! They're still around, and still making similar quality tools, but with so much shite around they're looking better and better! For some reason, a lot of folks seem to buy Taiwanese tools from motor accessory shops when they could get decent King **** for similar money! Weird!
Snail Brand are solid enough but they are what would be termed 'industrial' tools! Fine for doing up a bolt on a building site but not quite what a serious mechanic would need!
I can recall seeing Eagle occasionally, but not much about 'em!