Don't waste your time with Simple Green, it's too weak to take paint off minis. quickly. I tried it by soaking some GW plastic minis. in it and after a day it had done nothing.
Sounds like nevinsrip has used Pine-Sol quite effectively, could go with that.
Me personally, I took those same GW plastics and on the advice of an online forum tried Super Clean. It might also be under the name, "Purple Power" or some such name like that. In any event, it's in the automotive section of Walmart. It comes in a purple container and it meant to be an automotive degreaser.
This stuff works AMAZINGLY! I had primed the GW plastics with a spray primer that just horrifically caked and textured the minis with a horrible finish that was dried on like rock. Must have either been the temp. or a bad can of spray, don't know.
I put the Super Clean into a large tupperware container and simply put in the minis. and let them float around. For one bigger mini. I had to put a weight on the base to keep it submerged. Then I went back after a few hours and flipped over the floating ones just to make sure that all sides of the mini. were submerged for a time.
After letting them soak overnight this way, that rock-hard primer had literally dissolved and dispersed into the Super Clean. The plastic itself was not harmed in the least, it does not affect plastic unless you literally soak a mini. for a month in which case it might start to break down the plastic. But for a day it's totally fine!
I had to do very little toothbrush scrubbing, most of the primer had been degreased and broken down to the point where I could run the minis. under warm water and most of it just washed away.
***One important note. You may have some areas on plastic minis. where there's a light, chalky residue left behind from the primer. Even after you lightly scrub the mini. you may have some of this left behind. This is OK. It's like a "shadow" left from where the primer was originally bonded to the plastic. Don't worry about this! You can prime and paint over it again!
***MORE important note. WEAR GLOVES when using Super Clean! It works great but it's nasty stuff. The degreasing agent in it is powerful and not great for human contact. It will dry out the skin on your hands and cause a horrific itch that will take a couple days to go away if you get it on your hands. Even when I was using gloves some managed to creep in underneath and get on my fingers, so I had to use skin cream for a day or two to get them moisturized again.
But you can't go wrong with Super Clean for stripping, give it a try!