Good Morning Larry,
I've used Vallejo paints for years and they are my first choice for modelling. However, you need to learn how to use them. I spent some time learning how they "worked" by brush painting and airbrushing them until I was satisfied I could use them well. This takes time, and in my view is necessary regardless of the manufacturer and whether the paint is enamel or acrylic.
First, I use Modelcolor only, and thin it to the right consistency with Vallejo's own thinners - the clear stuff not the older milky thinners - and some Kleer to make it a bit more robust. Unlike David I don't use anything other than Vallejo's own accessories such as thinners ect. The only exception being flow enhancer (see below).
Modelcolor is quite thick so start at 50-50 paint to thinner and add more thinner until it's sprayable to your satisfaction. Search for table produced by Ultimate Thinners in the UK, it gives ratios of paint to thinner for a range of acrylics in the UK. I think it says the ration for Vallejo should be 30-70 paint to thinner for Vallejo, but I've found this a bit high. The trick is to experiment
If you find the paint dries on the tip of your airbrush then add some flow enhancer, either Vallejo's own, or Winsor and Newton. A couple of drops is usually enough, and make sure you do not add too much or your paint will "spider" when shot through the airbrush.
There is a difference between drying and curing. The paint dries quickly but it takes some time to cure, just like all other paints, and it is fragile until fully cured. In addition, as David said, it doesn't sand well, this is because I think it is vinyl acrylic and more likely to peel than sand; this is why I add some Kleer to the thinned paints. I would add that it does sand pretty well when it is fully cured.
Vallejo are great paints, and for ship modellers there's the equivalences chart published by an IPMS modeller. It takes time to learn to use them properly, but they are worth sticking with particularly if you want to shift from enamel to acrylic.
If you find you don't like Vallejo, try Lifecolor paints. I use them too, and what I've written above holds for them as well. However, they are better airbrushed than brushed. I've never managed to get a good finish when using an ordinary brush with them.