The cool thing about Anti-protons is that you can scale the proc. With any other weapon, you have a 2% chance to proc, but with antiprotons you have at least a 2% chance to proc. Spec into Attack Vectors and you can boost that by another 4.5%. Also spec in Combat Maneuvers and Battle Strategy and you can get another 4% from APA if you're a tactical captain.
So an admiral can have a 6.5% chance to proc, 10.5% if they're tactical. If I run 3 dual heavy cannons, I have a 48.6% chance of scoring at least one critical hit per salvo, and a 12.42% chance of scoring at least two. Granted, that doesn't factor in defense/accuracy, but it also doesn't factor in CRF.
Thats just looking at the chance to proc. The proc itself is also percentage based, so as you boost your weapons performance, you also boost the value of the proc.
Anti-protons are expensive to spec into, but the benefits can be huge, unlike the fixed procs of plasma, tetryon and polaron.