I personally love Contrast, but the thing is that it is a tool in the arsenal rather than something I would use exclusively to other paints. I love to put a layer of contrast on top of a zenithal'd model, but then I go over with more opaque colors to draw out details and highlights. Currently working on an Ogor, Idoneth, Rebel Alliance and Death Guard armies where I use contrast strategically.
There are few clear winners in the Contrast paint range:
Black Templar
Snakebite Leather
Guilliman Flesh
Skeleton Horde
Honorable mentions:
Volupos Pink
Nazdreg yellow
Wyldwood
Personally I find the best success with Contrast when I layer them with other paints. You also sometimes need to tone them down to not get the "candy" look you sometimes get with Contrast. I painted a ton of Poxwalkers using Plaguebearer but contrasted it further by using Agrax Earthshade on top.