I started out just like Bengt, and about the same time it seems. I've tried a bunch of different ranges, and really like mixing and matching - they seem to each do Something really well.
Army Painter does really good washes.
P3 does really great reds, white, black and odd colors, also it goes on very smooth and is optimized for wet blending. Just stay away from the metallics.
Reaper master has the very best flesh tones, and is also optimized for wet blending. Adamantine or Blackened Steel are the best metallic shadows.
Valjero has an enormous range. I like their new 'heavy' greens and greys, and use a lot of their metallics. The metal medium stuff is the ultimate metallic highlight color, and Iraqi Sand and Burnt Umber from the model range are really nice earthy browns. They make fluorescent colors which are very bright but don't cover very well - try adding a bit of white to the magenta for a screaming pink. And they have an extensive range of effects; crackles and blood and oxidation and stuff.
Foundry paints have really interesting earth colors, the bone and linen triads are superb, as are some of the greens and blues. The quality is really shaky in others though; the metals are almost as bad as the p3 metals, and some of the reds are atrocious.
As for the new gw range?
Well, I'm pretty sure if you dry it really well, grind it up and add a bit of it to cement, it could conceivably be used to fill out potholes.