If you're looking for distance kills, the AMR works far better (I am baffled why they didn't put a better scope on the railgun). I focus on medium and up-close kills. To aid this, I have practiced rapid reloading after every shot. For anything less than hulks, unsafe mode will one-shot them. Hulks can be one-shot through the eye. Anything bigger (turrets, tanks, etc) need to target weak points.
I had hoped that the Epoch would be a bigger railgun, capable of taking out big enemies easier, or possibly dropships and foundries, but I have been sorely let down.