I hear a lot of people praising dropper bottles for paint. In fact, they're the bottle of choice for most miniature paint companies, as far as I can tell. Everybody but Citadel. Citadel uses little plastic pots. You shake them up, pop the lid open, and touch your brush to a sort of shelf built onto the pot lid, which has paint on it now because you rigorously shook the paint pot for a full minute. So who's right? Everybody or Citadel? Here are 3 reasons I prefer Citadel's paint pots to dropper bottles for my miniature paints.
1. Drop or brushful
People seem to like dropper bottles because you can produce a predictable and consistent amount of paint from a dropper. This is useful when you want to mix paint. You can remember a recipe for a specific shade or hue by knowing how many drops of one paint to add to another: one drop of yellow to one drop of red, two drops of white to one drop of green, and so on. That's the theory, anyway.
The problem for me is that I often don't need a whole drop of paint. What I really want is a brushful of paint: the amount of paint a brush can hold. To get a brushful of paint from a dropper bottle, you generally have to put a drop of paint onto your palette, and then load your brush from it. The paint left behind is wasted.
Also, I think people are probably over-estimating the consistency of "one drop". A "drop" is not a scientific unit of measure, and to me there's not a significant difference between the concept of a drop and a brushful. A ratio of paint is basically the same whether it's one brushful or one drop, and a brushful is very often all I need.
2. Evaporation hypothesis
I can't prove it, but I feel like the paints I own that come in dropper bottles get thicker over time. Maybe my tolerance for how thin a paint is has changed over time, but I honestly feel that most of the first set of Vallejo Xpress Color paints I purchased were almost water-thin. But now when I use them, I feel they're all universally a syrupy consistency. Unless my definition of what a thin paint is (which is possible) has changed, I've begun to suspect that the paints in dropper bottles have been slowly evaporating and thickening. I know it seems unlikely because the dropper bottles are kept closed, but by comparison the first Citadel Contrast paints I purchased, well before I knew about Vallejo Xpress Color, are still as thin as ever.
It's gotten so noticeable to me that I've been adding medium to my Vallejo Xpress Color before using them, which I never used to do.
I haven't done any scientific tests on whether my hypothesis is correct, so I wouldn't defend my suspicion about evaporation if challenged on it. Maybe my complaint is actually that over time, I've come to prefer thin paints, and I'm finding that Citadel Contrast tends to be thinner (depending on the shade, because Black Templar and Black Legion are both thick compared to Ork Flesh or Pylar Glacier) than Vallejo Xpress Color.
Or maybe it's all in my head.
3. Paint cake
This one definitely isn't in my head, and here are the photos to prove it.
Dropper bottles are often praised for being the tidy alternative to poorly maintained paint pots but I have not found that to be universally true. For whatever reason, by Black Lotus and Space Grey paints from Vallejo Xpress Color consistently get a build-up of mostly-dry paint residue inside and around the caps. The Black Lotus one was at one point even worse than the photo depicts, and I've already cleaned it once. I can't find the cause of this, and I don't hear anybody else complaining about it, so maybe I got a bad batch.
I once theorized that maybe these two paints are plagued by residue because they're two paints I use frequently. But I've been using Velvet Red for my Adeptus Mechanicus army, and both Copper Brown and Wasteland Brown on my Roman and Egyptian armies, and those paint bottles haven't had accelerated residue.
Another theory is that it has something to do with the amount of pigment in the paint. Space Grey definitely has a dark pigment that tends to float to the top of the bottle. You can see it in the bottle, and so it's one of those paints that you really have to shake more than most others before using.
I'm not really sure, in the end, whether it's defective bottles or paint pigments or frequency of use, but my dropper bottles are definitely not as tidy as people seem to say they should be. By comparison, all my paint pots (aside from the ones I've let friends use), regardless of how long I've had them or how often I use them, look as good as new.
Counterpoint: Spillage
One thing that a paint pot doesn't do, that a dropper bottle definitely does, is resist spillage when you knock them over. You can knock an uncapped dropper bottle on your carpeted floor (I wouldn't test this, though) and not panic. Maybe a few flecks of paint get knocked off the bottle, but the paint stays in the bottle.
With a paint pot, there's no protection. You knock it over, you have 18 mL of paint on your desk or your floor or both, an no more paint in the pot.
Counter counterpoint: Close the lid
I say there's no protection against spilling a paint pot, but that's not entirely true. There is a protective device included with every paint pot, and it's the lid. Close the lid after you load your brush, and you're protected from spilling it. That's not always convenient, but I think this is why painters use a palette. Transfer a brushful or two of paint from the pot to your palatte, then close the lid, then paint.
An additional form of protection is a paint pot stand. You can find these, sometimes, made out of MDF or as 3d printable items, or you can just fashion your own out of something. I sometimes use those little tiny cups that hold tomato sauce in take-away, but I turn it upside down and cut a paint-pot-sized hole in the "top" (the bottom, turned upside down). The idea is to put the paint pot into something with a broad base so it's harder to knock over, even if the lid is left hanging open because you're too busy painting to close it. Essentially, you're adding buttresses to the paint pot. It works.
The winner is...
So I have to admit that both droppers and pots are functional paint-delivery methods. They both work, and they both have advantages and disadvantages. If you have two very similar paints, like Citadel's Khorne Red and Vallejo Xpress Color Velvet Red, I would choose the paint pot. I have evidence of this compulsion. I own both Citadel Ork Flesh and Vallejo Xpress Color Lizard Green, and I find myself reaching for Ork Flesh exclusively for the luxury of the paint pot. I find it more convenient. When given the choice, I use paint from a pot over paint from a dropper bottle. And to be honest, I've caught myself slowly replacing some of the Vallejo Xpress Color paints I use most often with Citadel equivalents, and I've come to recognize that I'm doing it for the paint pot.
That said, some Vallejo Xpress Colors are either really unique or else they're colours I don't use often enough to care how I interact with them, and they're half the price of Citadel Contrast. So sometimes the dropper bottles win, although never because they're dropper bottles. When I buy a dropper bottle, it's because the paint inside is paint I really love.