I think most paint lines are pretty good nowadays... I mostly use Vallejo paints though have started adding Scale Color, which I really like. They have high pigment density so are great for glazing, and dry super matte. GW paints are good, but like people have said their bottles are craptacular. I use their shades and Contrast (stupid expensive but pretty useful) lines as washes and glazes but am transferring them over to dropper bottles. Next time I order paint (afaik there isn't a decent source for paints in Portland/Vancouver so I mail order) I'm definitely going to add in some Pro Acryl -- I hear their Titanium White is awesome.
I tried a few bottles of Army Painter but didn't really care for them, the colors I had were pretty thin and chalky but I probably just got unlucky. Every paint line has great paints and stinkers, I probably just chose the stinkers. AP has a lot of fans so they must be alright.
If I were starting over, I don't think I'd buy a mega-set. I suspect there's a lot of dead-wood colors I wouldn't use very often. Maybe I'd pick up a basic set and add to that depending on the colors included.