I've been liking the Vallejo wash line, but I mix it 1:1 with Pledge to get good results out of it. Availability of paint is likely the biggest factor. As much as I want to try Reaper, P3, and Coat d'Arms I'd need to order them online. GW, Golden, and Vallejo (Panzer and Model ranges) are my only local choices. I airbrush with Vallejo, and any non-airbrush paint I have is to make colour matching easier. Golden I use more for mediums and some different things. I like the GW line, especially after the revamp. Only use the layer, bases, and washes though. The new washes work far better. There new technical line is interesting and I've tried the cracked earth effect. I know how to achieve a lot of those effects with medium mixes, but crackle medium is giant pain to work with on its own.
The only thing I've ever seen used from Army Painter is their quick shades and Sprays. Both get pretty good results and I know several undead players who only have painted armies because of the bone spray.