top cert out there is NASM(national academy of sports medicine). covers everything and really works well with building programs and sticking to a protocol. their basic CPT is very good, and they have multiple others that go above the basics.
another great cert is ACSM(american college of sports medicine). again covers everything, but is very clinical and covers a lot dealing with contraindications.
if you have a 4 year degree, i would look into getting your C.S.C.S. Its a strength and conditioning cert that is going to go above and beyond.
Cooper is a blow off. If you have any knowledge of the body and how it works it will be an honest waste of time except to get the piece of paper. Goes along with ACE(american council on exercise).
If you are seriously interested, i get good discounts on pretty much all of them through my job, and can help you out.