I always thought that fillet lugged was easiest, and it doesn't generally impress me much. As far as mitering, any bike made by someone that isn't an idiot will have well mitered joints.

As far as what joining method to prefer, it looks like with the heat treated materials, TIG is superior, but not by much. I have never heard of any problem brazing chrome moly except here. Hydrogen embrittlement seems like something that is fairly common in welding and not likely in brazing. But generally, I would say frame failure is way down on the list of things to worry about. I have seen failed frames, i think it was more likely with frames made by the guys that put the tubes in an open-hearth blaze and used brass.