Simply put:
Infiltrators have no spells, but they are quick and they hurt like hell. They are better tanks than Albion's armsmen or paladins.
Nightshades don't hurt as much with their weapons, but they have spells to help them out (direct damage spells).
Shadowblades aren't as fast or stealthy, but they hurt more. They have "left axe" as opposed to "dual wield" or "celtic dual," which, as the name implies, means basically that they use axes instead of swords or whatever.
In conclusion, be a Shadowblade, because Albs are stupid zerging teacher's pets who think they're better than everyone, and Hibs are drag-queen fairies that prance around a happy-go-lucky world full of giggles and butterflies.
:)