I've used almost everything out there from brake fluid, purple power, oven cleaner, to the expensive AK paint stripper that works super good but is super expensive, and comes in a very small bottle (about 3 fl.oz.
My go to right now is Stripwell.
It works great, reusable, and fast!
I've painted and repainted a car body 4 times in the same day trying to get the base, flake, and candy color correct.
That's 4 times in one day guys!
Yes, it's a little pricier, but you get a good amount of product, and its reusable.
The liquid I'm using right now il black from all the uses, and is about 3 years old. It's still just as strong as day one.