For color neg masks I would choose either FP4 or TMX. Delta 100 might be OK but has a very long
toe to it. You can try Ctein's Muir Softshot or my own tweak which he has also tested and is
simpler, consisting of very dilute HC-110 with a tiny added pinch of benzotriazole as a toe cutter.
And whatever film, you need to be sure any antihalation dye is thoroughly removed during washing.
For color negs you want a very low contast mask, preferably with a straight line response. Once you
figure this out for basic contrast reduction masks you can make interpositives and then mask them
for contrast increase masking. But you need to carefully balance your colorhead in order to get a
consistent response to all colors in the original. More involved than masking black-and-white originals.
Please be more specific for the developer. What is the exact dilution from stock solution and how much benzotriazole? I am not dead set on Delta 100, I am just looking for films that are of good quality with fine grain and good reciprocity, yet available in 8x10.