Alright, I'll go against the grain and say ARC. I am one of many folks who use ARC preamps with Pass Labs, and I am very happy, I think they blend very well.
The Pass Labs house sound is very full and warm, while the ARC sound is high resolution.
In my opinion, all ARC is too bright for my tastes, and all Pass Labs is too dark for my tastes. Together, the balance is just right.
Obviously, others will have other opinions.