I'm a big fan of Battlegroup. Love the system, it creates interesting games every time out. I use it for armour only 6mm games but I don't see why infantry couldn't be added.
For miniatures, GHQ are by far the best tanks out there. The detail on GHQ tanks is absolutely astonishing! Infantry wise, Baccus is my usual go to. Given, I don't have any of their 6mm WW2 stuff yet, I have 1000s of ancients and some ww1 stuff and the models are lovely! Baccus is coming out with tanks now as well, I haven't purchased any as of yet.