In my Saxon campaign, I used a lot of Fyrdmen. There's very little point bothering with the normal spearmen as their upkeep is far higher if I remember. When armoured spearmen can be trained, it makes sense to use a few of those thanks to their better defensive values, but still Fyrdmen make for good cheap fodder whilst the Huscarles and Horsemen do the real work. Fyrdmen's low costs make them suitable garrison and reserve troops too. Spearmen are a bit expensive for that.