[ultraman zoffy]

Testors Model Master acryl is probably the best paint I work with. As a brand, the only issues I've run into with them is their comparatively small color selection (brands like Citadel and Games Workshop have huge color palettes, but their paint sucks), and also, sometimes different colors of theirs have different properties (their pinks and purples seem very watery, and their light flesh tone paint tends to dry out in the jar easily).
No matter what brand is used though, surface prep is very important... thoroughly wash the figure/part first with warm water and dish soap. I also prefer to do a base coat of duplicolor vinyl and fabric spray paint on customs which helps adhesion and is very durable.
Honestly, I could go on and on about all the techniques and tricks I've learned the past 4 years of doing custom work, but I don't want to spam the board... Lol. If anyone has any questions, pm me and I'll be happy to try and help! At this point, I've pretty much got a solution for everything someone would want to do for a custom. =)