I have no experience with Reaper Master paints, but I used some of their regular jar paints some while ago and they were of a decent quality. They are acrylics and of the type you thin with water. Im sure Reaper may sell a solvent for them as well.
Vallejo paints are excellent and I use them a lot for 1/35 work. They are an interesting paint. You have to thin them slightly (again with water or Vallejo thinners). They flow smoothly and have very opaque pigments for the most part. You can thin them a lot and they shade becomes translucent, but the color does not change. You can build up layers of color with multiple applications. Vallejo's metallics are also very good for acrylic metallics. Their special alcohol-based Super series has very bright metallics. Super Silver looks like chrome on small applications. Vallejo also has things like a black shading set with various paints used to shade and hilight black! They also have some good shades in their Panzer Aces series, like multiple shades of rust.
I use Freestyle from Kitbuilders magazine mostly but recently purchased a large selection of Vallejo off eBay. Since the type I bought are for miniatures the paint is generally relatively thick. But as mentioned above I am using it with whatever amount of thinner is needed to airbrush and it seems to work very nicely. One nice thing is the multitude of colors available. I am still planning on picking up some from other companies as well mainly for color variations. The Freestyle paints I use can be air brushed from the bottle as they are formulated that way. If you want to look at them they can be found off the Kitbuilders main web page. I phoned in an order both times and she shipped them very quickly.