First of all you should consult your vet before administering any ointment to your cat.
BNP IS a triple antibiotic ointment, Vetropolycin is a combo as well I believe- if you read the tube is should tell you exactly what is in it.
I am not familliar with Terramycin but again it should say on the tube.
No one is really stronger than another, it all depends on what bugs you are dealing with, some bugs are resistant to certain antibiotics. Some atibiotics kill a broader spectrum of bugs but won't touch others. Some kill intracellular organisms like chlamydia and some don't.
Anything with an H on the label (BNPH, VetropolycinHC...) has hydrocortisone in it. This is a steroid to take down inflammation which is great- unless there is any damage to the cornea. Steroids decrease healing and can turn a small scratch on the cornea into a huge ulcer very quickly.