I'm fairly new, so mostly free killers for me, but if you couldnt guess from my username Huntress is my first love killerwise. I tend to run her with Bitter Murmurs, Huntress Lullaby, Fearmonger, and spies from the shadows, but I've been experimenting with the perks I just unlocked with event buys.
My new killers are Artist, Hag, and Dredge, out of which I think Artist is my favorite. Her perks are amazing, so I tend to run Grim Embrace, Pain Res, Spies from the Shadows, and Agitation. I tend to swap Agitation for whatever perk im experimenting with though. Hag I like Third Seal, Pentimento, Hex Ruin, and Agitation again, but I'm still figuring out the cute swamp Lady.
Aside from those I still run Billy and Trapper a bunch. Getting a good game with trapper makes you feel like a genius. For him I dont like to be a basement trapper so much so I run Unnerving Presence, Agitation, Huntress Lullaby, and Brutal Strength. Billy I need to rework my build now that I have better perks, but usually for him I run Tinkerer, Enduring,