The best product is in my opinion "Biostrip20".
It works on metal and plastics and does the job super fast while not leaving a bad stench. It's not even harmful for the environment!
I usually put a couple of metal mini's together in a cup and fill it halfway up with Biostrip20. I let it stay there for an hour and then bring the mini's to the tap.
Then with warm water I wash off the Biostrip20 while scrubbing with a toothbrush. Within 1-5min (depending on the complexity of the model's angles) you can easily scrap off all paint of any model.
In 20% of the cases there are still a few spots left because of thick paint that had been under it or complex angles that couldn't be reached that easy. In those cases I just put them back in the dirty Biostrip20 leftovers from the cup and repeat the proces half an hour later.
It's really, really a great product and I use it all the time.
If you are really curious I could try to film it the next time I strip models to show you how easy it is.