Overall Tamiya is the most airbrush friendly paint. One thing is important - forget what Tamiya says about being an acrylic paint: the term is ambiguous. Tamiya is much closer to lacquer because it's base (or medium) is made of solvents and the pigments are made with dyes. Your first clue is to check the bottle: flammable? toxic? then you've got a lacquer. It's a very mild paint and most modelers find it easy to work with. However, it's will help a lot, especially if you're doing "modulation" or very low psi fine detail work, if you use Tamiya's own (Gunze is a similar paint and its thinner works very well too - never use hardware thinners) lacquer thinner. Just as cheap, mucho better. I think people that use acrylic thinners (basically ISP with some conditioners in it) are so good with the brush that they could make anything work. Lacquer's better - period.
I've almost quit using Tamiya even though, as noted, it's the best for airbrushing. True water based paints like LifeColor, Vallejo, German Revell Acqua Color (or my favorite - Golden High Flow) are true acrylics. You could drink the stuff and not die. They have both natural or man made pigments (not dyes) and it's suspended in a liquid polymer. How much water is bonded into the polymere determines it's viscosity. So Vallejo Model Color is fairly thick and absolutely needs thinning. Vallejo Model Air has already been cut and is almost, but not quite ready to go. You can use a small bit of water to thin them - but I'd use their own thinners for thinner types (I'm almost sure Vallejo Airbrush Thinner would work fine with Lifecolor.) If you're going to airbrush Vallejo Model Color (or Golden Fluid) you need to get into acrylic mediums - airbrush medium - available in any art store - should be enough. Any reason to use it? There's no odor (don't forget to check the pigment - some naturals like zinc are not made to inhale), clean-up is a breeze and once you get used to it so is cleaning the airbrush. (Don't forget to clean it though - when polymere dries, it's touble to remove, although it can be done.) The water based paints are also far better than Tamiya for brush paint. You can also mix them - even across brands. I would not mix Tamiya with anything other than Tamiya - certainly not a water based acrylic. They look a bit different on the model, although it's subtle. Water based are extremely pigment rich, but will vary a lot of transparency. (Vallejo has less so than Golden.) Tamiya is more uniform. But not entirely - black covers better than yellow in any paint. The effect I'm thinking of is subtle but you can see it if you had a model painted with Tamiya next to one done in Vallejo or Golden. Tamiya's solvent base is very fine and when the paint is laid down (two coats is just fine - probably better for most purposes) it looks as though the plastic has changed color. Water based have a film - like real paints on real planes, tanks etc do - it it looks like an object that has been painted.
If you a color nut, Tamiya has one extra problem. They have enough colors so you can get ballpark on almost anything you need. But both LifeColor and Vallejo have more colors specifically aimed at military (or figure) colors. (LifeColor is rapidly building up the biggest "camo set" collection on the market and their colors are good.) If you lean the simplest paint mixing techniques, you can solve that problem. Tamiya mixes fine with Tamiya.
Tamiya paint is the most widely used in the world and I think it deserves it. There's no reason you can mix Tamiya and water based paints on different layers on the same model, so you could use Tamiya for a very nice base and use Vallejo for chipping. But the water based - once you get past the learning curve - have their own appeal. Non-toxic, no-oder, beautiful colors and excellent for hand brushing. It depends on what you like about modeling I'd say. Personally I like junior high art classes, and water based paints are great for futzing with. But if the paint is a simple tool, Tamiya is hard to beat.
Eric