After several thousands battles online I've come to use Men-at-Arms 3 ranks deep, set on Hold Form. The 3 ranks makes them 20 wide (on normal size units) and presents a wide front to deal with, while the 3rd rank (and Hold Form) allows them to take a charge quite nicely.

I rarely use any spear-carrying units, swords are so much better. So my main line consists of 5-6 MAA placed very tight. The Hold Form reduces fatigue and when kept together tthere is almost no opportunity for the enemy units to get a flank bonus.

The 3 ranks also compromise well the length of my main line. You want your main line long enough to make flanking the ends harder, but not so long that if the enemy overloads one flank your guys on the other flank have too far to travel. This is really important in 4v4 online games, probably less so in SP.

I use my footknights a little differently. If the enemy is cav heavy, the footknights stay 4 deep (Engage-at-Will), if cav light/inf heavy, then I go 2 ranks (Hold Form).

ichi