My favourite shampoo is Dodo Born to be mild. Doesn't leave anything behind and is nice and "suddy". Bilt Hamber Autowash is well regarded too and I'll get some of that soon to try. Try to avoid the shampoos with "added gloss / wax" etc as there's no point decontaminating and claying only to wash it again a put something back on.
I assume you're using 2 buckets for wash? If your car isn't covered with an inch of mud, I'd snow foam on a dry car as it'll linger a bit longer if it's only mildly dusty / dirty.
If you want to go all out decontaminating, then try a tar remover such as TARDIS before using the iron-x, then Clay. I use the G3 clay mitt after Tardis and Korrosol and it works really well.