[I was asked about this in comments recently, and wrote this all out. I figured it might be more generally useful, so I'm putting it in a journal entry.]

I bought all my gouache/watercolors like three years ago and the shit just keeps going :) I may have to replace paints this year :P

I don't think any particular brand is better than another, they each have different properties that can be useful.
So far, my box contains (by brand):

Acrylica - Made by Holbein Works (a Japanese brand). This is a kind of nice creamy gouache made with acrylics, so when it dries it resists reactivation with water, but you can force it if you scrub at it. It's not like actual acrylic paint that becomes inert. I like to use this stuff most as the workhorse, particularly for the lighter colors since it's nicely opaque! It's not cheap, sadly. I have warm and cool versions of the primary colours and a warm and cool white. I burn through these quickly, unfortunately, but it's the basic paint for me. I usually goop out this stuff and then alter it with one or more of the following to get what I need.

Reeves - Crappy student grade gouache. Kinda grainy, but it's cheap, useful for tinting the Acrylica when I want to keep things opaque and don't want to waste a lot of Acrylica trying to adjust color. Sometimes useful on its own if I want something ragged or I can't find the Acrylica tube I want quickly. I have a bunch of random secondary colours in this stuff. Reactivates with water easily, so I let it accumulate on my palette and just brush the dried gob with clean water to get it back.

Van Gogh - A line of watercolor paints made by Talens (a Dutch brand). These are very good, and a little goes a long way. My 0.3oz tubes are only half-empty now. It's very concentrated: add just a little water and it dissolves instantly. I mostly have blues and sepias in this color and use them for glazing or tinting gouache to reduce opacity. They work really well for me. All my price tags on them have worn off, so I have no idea if they were expensive or not, but they are worth it. The sepia and prussian blue are my go-to colors for tinting anything warmer or cooler.

Utrecht - A store brand watercolor from Utrecht art supply. Not great. They fill space in my box. If one comes into my hand, I'll use it, but the color is usually very thin and shrill. They don't resist further water at all, so if you splash or drip over it, it runs. If you try to dry brush over it, the paint will just come off. So it's kinda useful as a top layer for finishing details, etc. I do have a tube of titanium white watercolor that I like for mixing because it lightens and reduces opacity as well. The other gouache whites I have will lighten but still remain opaque.

I have a tube of actual acrylic paint in payne's grey, but I don't like to use it much because it's permanent, opaque, and dead when it dries. So I'll use it for knocking down mistakes to then paint back over or mixing in with my darker gouaches if I don't want them lightening up on me when I work over them.

I also have a jug of Golden brand matte medium which I typically will put over the initial drawing before I even start painting. Using a smooth/sponge or rough/crappy brush for this will texture the surface and give the gouache and watercolor grooves to cling to. This is also used if I'm putting down any sort of collage or if I want to mix with the paints listed above in a glaze. The stuff goes on white like elmers glue, but it dries clear (or translucent if mixed with the paints i use).

Also, lots of fixative or varnish sprays. I use these as soft "save points" while working, if I need to stop or take a break. They don't completely seal the surface, so you can always rework the paint underneath if you want to get at it with clean water, but they prevent incidental smudging or allow for mistakes with drybrushing to be wiped off.

Also my fingers, a lot :P Which is not good practice. So don't ever do it.

In general, I don't personally think it much matters what tools you use. Work within your budget and try to give yourself as many options for layering effects as possible. Get opaque and translucent paints, mediums and so on. Since all the stuff I use is water soluble, I do tend to mix and match it all together. There really isn't that much difference between gouache and watercolor. It's the same components just in different ratios.

Gouache is made from fat chunks of pigment suspended in a binding medium that dissolves in water. Watercolor is made from much smaller chunks of that same pigment suspended in relatively more medium. So if you thin gouache enough, you can use it like watercolor. And undiluted watercolor works pretty much like gouache. All of it will come back to some degree with fresh water and that's the point, to me.