I've been reading Grant Morrison's JLA. If you're gonna try it, start from issue 18, Synchronicity, and stop at number 33, Justice League vs Bruce Wayne. The rest is a bit so so. However, there were a couple of things that made he think he really got Arthur. As I mentioned recently, I love Arthur as King. He is royalty, he's not like the other Leaguers and his responsibility is on such a different level to them. These next two pages show this really well:
The first is from issue #2 of JLA v3. Arthur is overly pompous and even snooty and Diana is having none of it. I like Arthur like that, but I also like that Diana will not put up with it. She is royalty too, after all.
The second scan is from issue 41, towards the end of World War 3 and shows just how immensely badass Arthur can be.
This is definitely my favourite incarnation of him.