I use both. I do use a lot of layers. But if I’m trying to get an intense color, the water-paint mixture I load on my brush is goopy.
When layering, I’ve found that the biggest help is good paper - you want something that can stand up to the water and even some scrubbing without buckling. Being certain of what colors you want where helps a lot too - I always do an undersketch before painting, and (try to) know where my darks and lights are. That way you can put your colors on confidently, and not dab and mix until you’ve overworked your paper and muddied your paint.
For thicker paint, mix your paints up with water, or squeeze them out new from the tube, before you try to load your brush, so that it’s easy to pick up a lot of pigment. You can even put a wash of water on the paper and then squeeze watercolor pigment right out onto the paper!
Know your pigments. Some are more intense than others, some stain, some gallop, some crawl. Student grade is good enough for me, but others can tell the difference from that and professional grade. I use two palettes - my pure palette has very clear colors like winsor red, vermilion, nickel titanium yellow, cobalt and cerulean, and my dull palette has my indigo, raw sienna, burnt sienna, and sepia. I keep some alizarine crimson, cadmium yellow, and antwerp blue on both palettes. They’re good for different things, and I do mix between palettes some. I used to use Payne’s Gray on my dull palette, but found I could mix it from sepia and indigo. I replaced ochre and indian red with raw and burnt sienna some years ago because I liked their translucency a lot better. My cobalt sometimes separates a little, and makes weird dot patterns among the water-fringes. Other people I know have three favorite primary pigments and a couple of secondaries, or a palette of transparent versus more opaque, or cool and warm - find out what works for you.
Which brings me to my most important advice - experiment. Get paper, and find out how thick and intense you can make your paint. Find out what it does without trying to make a picture out of it. Take notes. The freedom of SCIENCE is worth hours of studio-time trying to perfect a piece without full knowledge of your materials.