I have played in a couple Iron Heroes games, though both as an arcanist (I ended up having to use the old character for the second due to time constraints), so I am not terribly experienced at building the other classes.
From what I have seen, the system is pretty self-explanatory; much more so than 3.5, the classes tend to do exactly what you expect them to do. The downside is that the classes all seem to perform pretty similarly - a bit of 4th edition syndrome going on.
I guess what I'm saying is pick the class with the coolest name, because they are all pretty cool, and it won't make too much difference. I am a great help, to be sure.