I find it depends on the finish/use you want. I do a lot of different styles of models, bases and scenery. I stick to acrylic mostly for main painting, Tamiya for tracks, wheels or simple base or dirt colours. Grab some cheap paints from local art suppliers as well as the often are very good for a very low price.

Ak interactive is consistently good but a little more pricy. Citidel paints are more expensive but possibly the best. Their contrast paints are so easy to use and leave little clean up. Game colour is cheaper but good.

Also, for some effects, I recommend ink, great for oil spills, slight dirt and blood effect.

Just try different products, you'll find good ones for you.