I believe there is no single manufacturer producing the best lights, one manufacturer might produce really tough lights but another company makes brighter ones for example.
I'd say these manufacturers are the leaders, in no particular order:
Fenix, Eagletac, Olight, Nitecore, Sunwayman, Jetbeam, Zebralight, Dereelight, 4sevens, Klarus, Predator, Surefire, Arc.
These are just the ones I could think of off the top of my head, I know there are many others and if I think of some I'll edit this post.
And another reason for me not saying who I think is the leader is because I know this thread will turn into a war of biased favouritism like the "who makes the best light" threads usually do.