stretching before makes no sense.. you should WARM UP the muscles, but save stretching for after or non workout days. take a yoga class on your off day
Dynamic stretches are okay before workout session but I would avoid any type of static stretching because it can tire out the muscles and possibly weaken your performance to some degree.
I believe in warm up sets before lifting, and stretching after training. Doing those will help prevent injury, increase blood flow to the muscles. Stretch the fascia after resistance training, and improve recovery
I always stretch really good after training for around 15 minutes. More than just a physical thing, it is a time for me to mentally reflect on the training session I just crushed.