If I am not trying to fight a pitched battle but just want the territory I like to send an archer in with centaurs and take out a weak enemy knight with the enemy usually retreating right afterwards. Set it up right and this can occur on the first turn you attack.
I really like high centaurs because they are also strong enough to put on the front lines. Just takes awhile to get them.
I also like bahamuts a lot - but it is hard to raise them. One of the reasons I like Dryst is because of the fact he starts with a bahamut and since Dryst has a power spell the two of them can put a world of hurt on the enemy. He also starts with a gigas which is handy if you are lucky enough to find a wisdom seed early in the game.
jectives
I think the neatest thing about Brigandine is the many ways you can play it. A lot of times I don't even really focus on taking territories but rather on having several groups of knights rampaging across the map.