By 'Citadel' do you mean
GW? Do they even use the name Citadel for minis production anymore?
I'm not sure. If you're interested in
FoW, the best advice seems to be your choice of either the Open Fire boxed starter or the base rulebook. I got the latter and a couple of the big theater books (Fortress Europe and North Afrika) from The War Store at a good discount.
On the other hand, the box set has a bunch of tanks in it.
I think it comes down to certain army configurations are going to be cheaper, but certainly not all.
FoW can be cheaper if you use other 15mm minis. As it's historicals, they're widely available and I believe the
FoW people allow them in tournament play.