I see people in Iron Banner using a wide variety of weapons successfully. The only one I don't see much of is the pulse rifle. I think it comes more down to finding what fits your style and learning to use that weapon effectively than to which weapon you use. Of course in Iron Banner the base damage makes a big difference as well, unlike in normal Crucible rounds. I recommend making sure you use a fully upgraded weapon that is at least legendary status if you want to be competitive in Iron Banner. Legendary and exotic weapons can go up to 300 damage, while all others are much more limited. Once again, this damage cap means very little in normal Crucible, but is huge in Iron Banner because of the level advantages.