I have had the tren cough with both the acetate version and the enathate version. I have also had it when made from powder form and pellet form. I just had it about 10 days ago, and I felt like I was going to pop a blood vessel in my head! It was good though because I had a chest cold at the time and it helped me cough up a lot of flem.
The fina cough is directly related to nicking a blood vessel on the way in. Everytime I have had it, I have always pulled the needle out and seen blood. The times I have not had it, there has never been any blood.
More specifically, the methylcobalamin form of B12 is recommended, as it has been shown to be the most effective. Taking B12 gives you a huge boost of energy while training, and more importantly, greatly helps your recovery.