Citadel base

I have used citadel, and testors model master's also I've used vallejo. My brushes shouldnt be the issue as I have very good brushes that I paid good money for. I want to try formula p3 paints as Dr. Nighatmare suggested and the actually have them at a comic shop near me. My only issue with mm is that they don't seem to cover as well as citadel as they are sometimes too thin. But citadel are often too thick. Lol its finding that smooth middle ground, that sweet spot I guess. What about tamiya? I've heard mixed things.

Brushes you can buy at discount stores work great, the only problem is that the bristles tend to fall out because of their cheap build, otherwise they work fine as long as they have hair bristles.

When you pay 8 dollars for a "good" brush, youre really just paying extra to ensure the bristles won't fall out lol, totally worth it though.

Anyway, I'd switch to Formula P3 paints, theyre a dollar cheaper and flow better. The color selection is limited, but you can mix to get any color.

Testors paint is usually more durable than Citadel, and costs the same or less.

To add what these guys said, it does make the world of difference for brushes. I no longer use Citadel paints (only because they were not being sold in my area at the time and I fell in love with another brand) but I really only buy their brushes. They are more expensive but I like how they apply paint and they hold up much better than the cheap brushes.

One thing that I would like to add that wasn't mentioned is that it could be your water. A lot of the more professional guys use distilled water to thin their paints or, as TXT mentioned, the brand of paint your using thinner. Sometimes, even though you may not taste it, your water might have minerals and chemicals that cause a negative reaction to the paint you are using.

I'll second what TXT said about brushes, you definitely DON'T want to be using cheap nylon bristle brushes, those are going to leave marks no matter what you do with the paint. Best advice is to invest a bit of money in some high quality natural haired brushes, maybe just get one larger brush first to test it and see if that's where the problem lies.

There's no reason you should be having trouble thinning down that paint with water. I do it all the time and it works perfectly.
You may be using a brush with bristles that are too thick or made out of the wrong fibres. Try getting a sable-haired brush.

For thinning the paint, I always have a 1:1 ratio with water. So for every drop of paint, add a drop of water.

Citadel also has a thinner called Lahmian Medium. Add a drop or 2 into your pots and give them a good stir.

Those tips should all help.