Since we are on the subject, for each race you should know your spotters and infiltrators. For example: Orks have Big Mek, Warboss, and mega armored nobz for spotters. Their infiltrators are gretchins and tankbustas. To learn more about them you can go here: http://wiki.reliccommunity.com/Dawn_...:_Infiltration
I hear a lot about using broadside battlesuits along with hammerhead gunships yada yada yada. I'd also like to mention that so many people overlook the Kayoon(patient hunter) command post. Not only do you get 2 tough units which specialize in melee combat but you can also upgrade many of your units' armor/health and sight/range enhancement at the path to enlightenment. It is known as patient hunter because it is more focused on destroying infantry where as killing blow(Mont Ka') is more focused on vehicles and buildings. By the way, if you don't have at least some melee attack units, the rest of your Tau army will likely get smashed quickly or sent retreating by any decent player.