The Inkbrush is designed to hammer home the swings, dip in and out because of decent refill times, and harass the turf with sprinklers and inkstrikes. On maps with spots that look down on set areas, swinging as fast as you can doubled with the sprinkler, can really help get that inkstrike up pretty quickly. It can be used offensively if you're a boss at hammering the trigger, but otherwise, just do your own thing and focus on the turf. And for those who say it doesn't work on Moray Towers... sorry, but it's all down to the player because I was fine with it~ :V
The Octobrush, on the other hand, is a tad more offensive. It's a bit slower in terms of swing action, and movement, as Tsukuyomi said. Nothing shines this point through more than the Kraken. Krakening through the attacking team isn't the only thing it's good at. So many times I've just plowed through nothing, got up to the enemy side, placed beakons in a reasonable area, and put the entire enemy team on red alert; watching them scatter trying to stop me, and also the rest of my team who come pushing up to my location. Played right on set stages, it can be a brutal mix; just remember, unlike the Inkbrush with the sprinkler, you have to earn that special on swings alone~
The one weapon you don't want to go against with brushes are blasters. For all the people going 'chargers are rollers worst enemy' keep forgetting the brushes aren't really rollers. I don't place them in the same category because they're supposed to be far quicker than rollers, so darting around makes a charger's life a little harder. Blasters, however, don't care about that; if it explodes and you're anywhere in the radius, it'll either slow you down or flat out wipe you out~
So yeah, my a little thing on the brushes~ XD