I'd have to say, during my time as playing as a Survivor, I love the encounters with the HK-SCOUTs, they're slightly smarter than a T-600, given their role as recon, but still "dumb" enough that you can easily escape if you don't make a lot of noise, run in the open, or shoot a firearm.

Had an encounter yesterday, where I was looting in the hospital when an HK-AEROSTAT (those small drones) spotted me as I was on top of the building. An HK-SCOUT that was nearby changed its patrol route to investigate. Very intense to slowly make my way towards an elevator shaft while avoiding the AEROSTAT and the HK-SCOUT, and escape through the sewers/canals.

That out of the way, what's been all of your favourite encounters so far, whether it was multiple, or just a particular skynet drone to encounter?