Personally, I would kick the spearman. He's a relatively squishy tank, and lightning spear isn't very useful by itself. Viking is handier, and you should always have a monk (especially if you plan on having a low mdef front line). If you don't go for stuns very much Arties are only good for DI, so it's a matter of how much you value that.
Lady Knight is better than swordsman (imo) so you can always get rid of his ugly mug that way.