For the love of your health, not to mention the environment, do NOT use brake fluid. It will melt plastic anyway.
Simple green is okay on some metals, but it takes a looooong time on well primed figures. It's not too good on plastics.
You need to tell us where you live, products vary around the globe. If you are UK based, you can try Fairy Power Spray, available in supermarkets, for decent results on both plastic and metal. Another reasonable product is Biostrip, google it, involves mail order and quite expensive, but will shift most paint, worth it if you have a large batch to tackle.
Couldn't agree more. Brake fluid is highly corrosive, toxic, bad for you, bad for models, bad for the environment, and all that's before we've tried to clean it up when we're done! It's also very expensive. It will strip paint, but it'l strip everything else it touches!
My personal favourite is a long bath in Methylated Spirit. Methylated Spirit (Meths, as it's more commonly known) is a denatured alcohol and pretty much pure ethanol. It is used more frequently as a fuel source for camping stoves and oil burners, but has great practical uses when it comes to cleaning (I clean the inside of my car windows with it because of a smear free finish), and stripping paint.
It's cheaper than most of the other cleaning products mentioned and beats nail polish remover hands down. After a long soak, an old toothbrush and a needle will get the stubbornest paint from chainmail! I mean what I say about long soak too, I accidently left plastic shields in a bath of meths for 8 months once. They were absolutely fine. The paint, sadly, wasn't. It works a treat on metal too, and is safe on most types of resin. I've not tried it on Failcast...*cough*..ahem...Finecast yet, so I'm not overly sure of its success.
Failing that, simple green is the best product from what I hear, it's just notoriously difficult to get in the UK.
I'm in Canada as well and I generally use nail polish remover for metals and Simple Green (you can find it at Canadian Tire among other places) for plastics. I've had some plastic models in Simple Green for over a year and nothing has happened to them. Its not the best stripper but if you ever have a plastic model that you glued wrong it can help. It turns the glue gummy and makes it easy to take apart the plastics.
For my resin dolls I use either Winsor & Newton Brush Cleaner or simple isopropyl alcohol. Acetone will pit and just destroy resin if left on it for any amount of time so be careful.
I use fairy power spray (in the UK) on all my models. You can soak them as long as you want and the models will never be damaged. The paint can be brushed off very easily after a good soak. I leave things for a week, but only because I am in no rush. Over night soaking is probably sufficient.
I used to use nail varnish remover, but it can start damaging the minis if left for more than an hour or so.
I've never had any result with simple green... Although it is a great general cleaner.
Plastic: Brake Fluid. I know everyones hating on it, I just use gloves and a mask. (My dad's a mechanic though so he can recycle it properly) Use the Gunk brand. I've left models in for up to 3 days. It disolves the glue sometimes but other than that no problems. Paint just flakes off with an old toothbrush. It also gets rid of PVA glue if someone made an ugly base.
Metal: Goof off works wonders! BUUUUT, Wear a mask, glasses and gloves! That stuff is nasty... and toxic. Acetone also works well but I find it doesn't get into the deeper details without soaking the models
I've heard oven cleaner works for metals too but I think it would be too risky considering the corrosive bases in it.
from my experience, a mix of simple green and 90+% rubbing alcohol (roughly 4 to 1, simple green to alcohol), and a 12+ hour soak will destabalize all but the strongest of paint bonds, and honestly, after 36 hours, i've found that next to nothing holds up. it does however leave an odd grey scale on pewter models which needs to be scraped away.