Now with the latest update by TC removing the Custom Escape maps , they have very nicely gave us another unwelcome grind for the 100k kills on Horde/Escape.
Currently i am using the map "The Detour" running Brawler class. Upon spawning i make my way to the end of the hive in the first chapter, bypassing a few of the safe rooms. Along the way you will either come across (Drones, Buzzkill Scions, Rejects and Leeches), or (Drones, Ice Scions, Rejects and Juvies) which are simple enough to deal with.
As you come to the very last Saferoom turn left and you come to a deadend, from which either Leeches or Juvies keep spawning around 7-8 at a time. I would recommend using the Brawler (My loadout is Defensive Tackle, Perk up, Soothing Warmth, Torch tackle and All the glory).. as you can use your tackle to kill them all, then rinse and repeat for a few minutes until the Venom catches up to you..at this point the enemies stop spawning.
I then just restarted act and done same thing again...on average i got around 700-800 kills per run with Leech spawns and 300-350 with Juvies, so i'd recommend Leeches.
Hope it can be of any use
https://www.xbox.com/play/media/64KQZ2LF