I use words.
I try not to use minatures as it makes people focus on them and make them think like a tactical minatures game rather than a roleplaying game.
That works for small skirmish combats where the opponents are roughly as many as the player characters.
But when you reach mass combats with up to and well over 20 or so combatants, miniatures can really help out in visualizing the situation.
It's just a visual tool, it doesn't necessaily make anyone confusing the game with a miniatures game. It's just that it can be pretty hard for both players and GM's alike to keep track of more than 20 combatants at once. Just imagine:
Player 1: I make a charge move against that guy.
GM: Which guy? That guy behind the wall, the guy behind the barrel, one of the three guys standing 40 feet away shooting at you with crossbows, the iffy mage-looking guy on top of those stairs seeming to prepare a spell, the five guys flanking you from that alley, the guy clambering over the fence or the guy with the cape?
Player 1: Erm.. Wait! I thought the guy in the cape were the one standing on top of the stairs trying to cast some sort of spell?
GM: No, the guy in the cape is the guy standing sort of behind two of the guys coming from the alley.
Player 2: Wait a minute. I thought the guy behind the wall was the one who accompanied those five guys coming from the alley.
Player 3: I don't know what the hell is going on at all actually.
In my opinion, combats in roleplaying games should be fast paced in order to emulate the sense of stress and urgency that comes with real world combats. When the average combat round takes up to an hour in order to explain where everyone is standing in relation to eachother and making sure that all the players get it, that fast paced sense is sort of lost. When you use miniatures all the players have to do is take a quick glance and act accordingly and stay in-character pretty much the full time.
Of course, if you know of some awesome and near mythical way of keeping track of mass combat between more than 20 combatants without having to turn the NPC's into charging idiots and the combat premises always constitutes the PC's standing on one end of an open battlefield and the NPC's always stand on the other end and they can all take pot-shots and charges against eachother in an unnaturally convenient way, while at the same time making sure that the players all get exactly where everyone is located without any confusion and STILL make sure that the combat plays out in a fast paced and stressful manner. Then please share this method with me, because it would certainly be helpful.