I have used both animal test and m-stak and originally found test to be far superior. I ran it for 42 days straight and made some great gains in size and strength. I have run m stak a number of times and was originally disappointed with it, but have since grown to love it. In particular, the strength gains are great. If you have never run either, my suggestion would be to get 2 tins of test and one m stak and run 42 days straight on test then use the m stak.