For the first time in my painting career, I used a GW Foundation paint.
Gasp! I know some of you all have been using them since they came out, but given my Dinosaur like nature, I'm slow to adopt new things. It took me months before I even thought about buying the new GW washes.
Honestly though, I'm not impressed. In fact, I found it a bit difficult to use. It was like painting with white (PVA) glue. Sure, it covered in one coat, but trying to get that stuff on the model gave me nothing but problems. And... I had to go back with a second coat that was thinned with water to get a smooth finish.
I only used the GW Foundation Tausept Ochre on the door icons on this model. Thank goodness I didn't have to use the stuff on the whole model.
I only own about 4 or 5 regular GW paints at this point. Actually I just bought two more regular colors the other night for the Storm Wardens project since I wanted my colors to match everyone else's. If I could have gotten away without buying them, I would have gone that route.
I normally use whatever it takes from whatever paint line it comes from. The main reason is, I despise mixing colors. I'll mix them for spot application on one model here and there, but I absolutely refuse to mix a color to be used on a number of models. I'll go buy something that is close before I go through the trouble of mixing. Yes, I am that lazy.
Almost all of my colors are your basic craft paints. Americana and Delta Ceramcoat are the ones I use most of the time. They're almost like GW foundation paints that have been thinned down a bit with water. Sure, some of them are transparent and semi-transparent, but that's yet to be a problem for me. In some cases, the transparency has actually helped with certain techniques.
In the end, I don't think it matters what kind of paint you use. Some paints will require certain "methods" of application for maximum effect, but as long as you're making the effort to get your stuff painted, that's all I can really ask for anyway.