I had also seriously considered Legatus Legionis. What does Pillage do, while I am at it (being a noob, that is )?
Pillage does two things. First, it lets you kill more population/create more unrest/loot more gold when using the Pillage command. This is of highly questionable value in most cases.
Second, and IMO more importantly, if a commander has it they're allowed to use the Raid command. Take a unit with Pillage (or give one without it an Implementor Axe) and shift-click on an enemy province within their movement range. This will let them "pillage" w/o capturing the province, and there's no guarantee that defenders will be able to intercept them (if they do, though, any raiders retreating from that battle will die). This also allows for pillaging uncaptured fortified provinces; e.g., that fat, juicy enemy capital. The interception rules are similar to stealth detection rules if I'm not mistaken, and there's currently an exploitable bug where raiding armies consisting entirely of fliers can never be intercepted (and hence raid with utter impunity). But basically Raiding is a way to weaken enemy provinces (yay unrest!) without capturing them, and is probably most dramatic if done by fliers or sailors (though again, it's exploitative to use fliers ATM). It's not a game-changer, but it's a nifty trick to have up your sleeve.