The busy backgrounds are a problem in the first two. I know how tough it is to get clean backgrounds at ALA (which is why I'm not there currently, actually), but there are a few ways of dealing with the issue. Using a longer lens from farther back means you'll pick up a much smaller piece of the background, which means you can angle the shot to find something less distracting. With the Batman shot, I would've waited for the guy in black to get out of the shot.
With a cooperative cosplayer, you can always take them a few steps away to a less distracting background, as well, or, if you want to bring gear into the equation, you could use a fast (f/2 or better) lens to totally blur out the background. An 85 f/1.8 or 50 1.4 is a great lens for doing just that.