My answer depends on if you are travelling with a companion or going solo.
If I'm alone the I prefer AC (or NZ if from LAX). The US new C looks very similar to AC but availability will be sparce.
If I'm on vacation then I like UA new C (767 only to/from UK), especially for the East bound overnight sector.
Trying out CO C GLA-EWR this year so will let you know.
I also love the new LX C (333's only) and TK's C (777's only) is great too.