That is pretty interesting topic, I mean the ways to do an AI. What I do is simply think how I want the particular "enemy" to react on particular player's behaviour etc.
Chase the player For instance I use Pathfinding combined with Line of Sight for my 2d action shooter game to make my horde of enemies to chase my player as soon as he gets close to them. So with combination of two behaviours my enemies have an AI to be agressive.
Attack the player For non shooting enemies I use "Is Overlapping another object" in order to trigger attack function.