Depends. As Germany, last campaign I did:
- lots of standard inf or mountaineer armies, which are either 9 divisions or HQ+8 divisions (or rarely HQ+11 divisions, but I find that is a bit wasteful).
- one or two 'breakthrough' armies (which are often HQ+8 tank divisions, or HQ+5-6 tank + 2-3 motorized) which will punch through anything and get the front moving (with smaller nations, I do only 3x tank divisions)
- if I have the time/IC/research, a couple of 'follow up' armies (9x motorized or HQ + 8x motorized, to follow the tanks)
I like the way that army layout plays. Lots of HQs boost supply, combat events, and help with command limits.
But I've experimented with all sorts of armies - a motorized, mobile, brigaded russian army (without the purges, meaning good generals) for defending vs germany (which worked suprisingly well despite not being overly huge, with some 100-ish motorized divisions, some tanks, and maybe 40-50 inf) where most of the mobile armies had HQ+3 tanks (w AC)+ 5-8 motorized (with SP ART) and some were pure 9xmot-sp art stacks.