As for warrens injectors and customer service, it is some of the best service I have ever come a crossed. I met Jesse is at some local pulls this year, chewed on his ear about being able to get ahold of them(I'd reccomend emailing pat) and he gave me his number and said text any time. I had two injectors go on me last week(my personal stockers) and all in can say is Jesse took awesome care of me. And man if you ever wanna see more 6.0 injectors than you could ever imagine, go to their shop.
Awesome guys, saved my ass all I had to do was drive down to them, about an hr and a half(traveling the speed limit lol). Plus it was cool to see jesses trucks the "shop/daily driver" drag truck and his puller, plus pats street/drag truck sweet set ups for sure.
As for holders I have only heard one bad thing jay at php sent ryklan his sticks and one had a bad fuel plate when he got them back, but it was taken care of in a very fast time frame. The only things that I see that set them apart would be warren has a flow bench, and holder has a bit more personal take since he's a bit newer and a smaller shop(injector building wise). But I would not be scared to have holders sticks in my truck. And end of the line I'll be running warrens since I can drive to them pretty easily.