Whether it's Vallejo or GW, you still have to water it down. As a rule, pro-painters will almost never apply "pure" paint to models. The exception being very tiny details, like a white dot on a gem. Even then, it's usually diluted 1 part paint to 1 part water.
I really suggest the Miniature mentor DVD series. The basic one will cost around 20-30$ and give a really good idea on how to use professional techniques. It has changed the way I paint completely. I use to put a thick base coat on my minis. Seeing a guy having to put 2-3 layers to get a full base coat raised questions, but I've tried it. It's just incredible how tiny details will show much more doing it this way.
As for quality, you can use Vallejo, GW, Andrea, it doesn't really matter. Some of the best pro painters in the world will use GW (Vincent Hudon come to mind). It's just a matter of dilution. Since dropper bottle tend to keep the paint longer that GW pots, you'll have to dilute them a bit less.
Also, there is the matter of how to dilute. A 2 liters bottle of distilled water costs about 1$ and will last a year. I might seem fussy, but even a bit of chlorine will mess with the acrylic mediums. A few dropper bottles (empty, 1$, from Vallejo) will be used to keep water, alcohol, "future" (than acrylic floor shiner that is pure acrylic medium). Those will help to dilute and keep a paint running. For example, diluting 3 drop of paint, 5 drops of water and 1 drop of "future" will make a good paint to blend and the future will act as a drying retardant. Washing with a bit of alcohol before you wash with a regular wash will help your wash to go into the recesses, etc...
I really started to get interested into painting techniques about a year ago. I'm fascinated by the techniques that change a "hobby" into "art"! There are a lot of resources out there and really learning how to paint is a thing that pays so much in the long run. I wish I'd studied all this 7 years ago when I started.
If Strewart is interested I could make a list of resources for a sticky...
Phil