Artist acrylics and fine miniature acrylics and such have finer ground pigment and more of it. This means they thin better and have better coverage (also why the previous post said to strain).
Most will thin with water and future or another medium (I've even seen people use stuff like windex). Some brands like Tamiya need alcohol instead of water.
Color itself also plays a roll because of the commonness of certain pigments. A dollar bottle of Apple Barrel Black is just as high quality as any fine brand because iron is so darn common and cheap. A good vibrant blue or yellow on the other hand is worth the extra cash.
Anyhow, when brush painting just remember the miniature modelers mantra "Thin your paints, lots of coats."
Forgot to add.
AppleBarrel:Cheap, good for basic colors like black and white so you can mix your own grays.
Ceramcoat:Similar to Apple Barrel but also has some good tans and earthy colors
Proper Tube acrylics: Very high artist quality. Needs lots of thinning
Coat D' Arms: Best metallics IMO. They used to make the Games Workshop paints up until a couple of years ago.
Reaper: Has some unique washes and mid hues you don't find premixed in a lot of lines. Their Buckskin is to die for.
P3: Good quality, I like their light reds.
Tamiya: I don't like dealing with "special needs" lines but their paint is top quality. Lots of folks swear by them.
Vallejo also usually gets a top recommendation but I haven't messed with them yet. That's the problem with getting a set of paints, you pick and choose select colors for projects. Honestly the stuff I go through the most is primer gray, black, white, gunmetal, and future. Takes a long while to chew through a whole bottle of color for me.