I have had some experience... DL BE, KLM WBC, and NW WBC (old & new).
In order of preference based on just the seat & IFE.
NW WBC (new) - almost lie flat, massage, large screen, VOD
KLM WBC - slightly more comfortable than NW's old WBC, ok IFE
NW WBC (old) - great barcolounger chairs but with no real adjustments, ok IFE
DL BE - a few more adjustments, but not suitable for anyone over 6' IMO... i had to prop my feet up on my carryon, ok IFE
I haven't tried CO or AF or KE yet.