Denmark has the best troops for fast early expansion.
Viking Raiders are like Zerg (if someone played Starcraft :P). They destroy every infantry in early period, and fully upgraded fight better then DFK.
There is really no needfor Denmark to use any oher infantry in a field battle. I usually combine them with Norse archers for my foot soldiers regiment, supported by some cavalry i have at the moment available.
This allows to use troops in all the battles so they gain expeirence fast. And almost every castle can retrain them.
The trick with the vikings is they have AP attack and are in number of 75 compared to a normal 60 unit. So they defeat even the JHI or VHI cos they out number them greatly.
Sadly there is little use for other infantry. Huskarls are better then vikings but are only 60, Norse Swordsmen ar just like Norse archers so no need for them. I use swordstaff militia in towns, but thats it.
If i face a cav heavy opponent i take them to the woods where the vikings shine even more.
If i have to fight in the open i just use some Swordstaff militia or some Obudashers instead of some vikings and norse archers.

Normal army: 6-8 viking raiders, 4-6 norse archers, rest flanking troops (cav or 2h axe)
Open field cav battle: 4 viking raiders, 4 norse archers, 6 obudasher, rest flanking cav