The only immediate effects for me in terms of muscle gaining are nice glycogen stores. Deca is usually pretty steady eddy, and probably the best long term bulker due to the recovery properties and the joint, healing stuff etc. Great for making long term gains bc it is super forgiving. If you get stupid and lift too hard for too long, you will most likely sustain less damage to your body, and when you discover the errs of your ways, the deca,for me at least, has always proved to undue the damage done by overstressing my body. While I like testosterone more, I cannot say that testosterone helps me heal better.