They are moreorless the same. Test E has a slightly shorter active life and should cause slightly less water retention than c. But to be honest that difference is likely to be minimal if noticed at all. So they are very very similar although test c is meant to have more of a kick. So don't worry about the difference cause if you liked test e you will like test c. I would actually say 6 out of 10 prefer c to e and 3 prefer e and 1 thinks equal. That was just an estimation of what I have heard in the past.
What brand do you have? I ask because that is where a difference in quality can be.