I dont have an opinion with either, if any person could possibly tell a difference I'd drink my own piss bear grylls style
I choose whiteline for my liberties simply because I can send an email and a new item and several freebies arrive within 2 days of any problems. When a bush flogs out they listen to advice and manufacture them better. Awesome company to deal with and responses to emails within all of an hour.
All up sitting 30 metres from me I have a Gen 2, 3, & 4 with a full compliment of whiteline gear and they all perform stellar once the alignment and spring rates are right. (the gen 2 I dont own)
But to think there is a difference in the quality or end result is laughable. I highly doubt AVO or cusco will supply me custom or prototype bits for when I need something on only a day or two's notice. Cant send them an email with a picture of a broken bit and magically new stuff arrives in the mail. As a consequence I'll always refer people on and continue to shop there. Aesthetically the cusco gear looks awesome and is totally pimp. For that reason alone I say go for it for those of you that care. My suspension bits are typically covered in dirt/brake dust/mud/tar so it doesnt worry me so much what color the paint is underneath

Cusco for looks, AVO for looks, whiteline for local service etc.