I think it is more important to keep layers of paint or coatings thin when you weather a model because you add many layers. If you are just adding a color I don't see an issue with any of the model spray paints or even the ones at Walmart.
Dave
I know some brands are better than others, and ironically the cheap WalMart brand paint that's been discontinued actually had the lowest flow and worked best for models out of any other brand I've used. At least in my opinion. There is definitely an issue with some of them, though, especially when you're working in N-scale. You can get by with a heavier spray in HO and larger where the details are more pronounced and don't get rounded off so easily. There's also a difference in what will work well with scenery and buildings as opposed to locomotives and rolling stock.
Testors primer in particular goes on so thickly that it looks almost like you dipped the model in plastic instead of painting it. In fact, it goes on thickly enough that I actually use it as a filler on kit-bash jobs, much like bondo is used on auto bodies. Just spray it on and wet-sand until smooth, and it'll fill in fairly large blemishes and joints. It's actually what I used to fill in the gaps between access doors on the long hood to convert a GP60 into a RP-M4C slug.
I have used Model Master rattle can paint as a color coat back in the day, and it did okay. At the time I thought it was fine. Later on as I got more into painting I needed to actually match colors to what Atlas, Kato etc. were putting out. This more or less forced me into using an airbrush and once you compared the two, you could see how the rattle cans, while not completely obscuring details, really did round off the details and make them less distinct. With the airbrush even the finest details still stand out clearly. And again, this is MUCH more noticeable in N-scale than it would be in larger scales, but even that is relative. Yes, it's very obvious under a magnifier as you work on applying decals and look at the paint job. Is it any more noticeable when the loco is sitting on the rails? Probably not, and a lot of the detail I strive for will probably never be noticed outside of closeup photos that I post here or something.
In the end, it just depends on how picky and anal you want to be about your paint job. I tend to be very much so on my locomotives, at least as much as my skill will allow. Meanwhile, my scenery is always going to look cartoonish and fake and oh well. We all care about different things, and what's super important to me would go completely unnoticed by someone else. Bottom line, I guess, is just to try both and see what looks and works best for you personally.
