sustanon has 4 esthers.. you will feel it quicker since it has 2 very short esthers and also it will stay in your system longer cause it has a nice 21 day esther.
cyp is 2 week esther.
sustanon hurts for most people cause of high BA content
cyp should be injected 2X per week 250mg each
sust can be injected just once per week at 500mg, or you can get away with 2X per week as well.
that is the main difference.. all in all it comes down to finding good quality test that isn't underdosed.