http://www.3gunnation.com/magazine
Here is 3 gun nation magazine.
Its geared towards the US and the matches they hold down there, but you can get an idea of what the top in the sport run.
Youtube vids of the big guys will show their equipment and some of the techniques they use.
There is no right answer as to what is best etc, but what seems to work for most is an AR15, a reliable pump shotgun or semi, and the pistol of their choice.
The KSG shotgun was mentioned.
I'm not convinced it is any better or faster than my supernova with the extended mag tube (that holds 13 rounds by the way)
I think a conventional pump is faster to load and use while on the clock.
The ksg has 2 mag tubes, a switch between the two and whatever else.
Plus to reload you have to reach all the way back to the base of the butt stock.
too many things that can trip you up when adrenaline is pumping and time is running.
Having said that, if you are not in it to win it, then use whatever you want, be safe and have fun.
The more people that take part in all versions of the shooting sports, the better.