Pvp changes tremendously once you start getting gold heros, not because of active skills but some heroes passives are just that much stronger than others. This may be a little different from what others may say, but I think the ability to stagger other heroes is one of the strongest CC effects in the game. If you are able to catch the enemy in a reload or channeling an ability, staggering them stops them and resets the animation, sometimes even wasting the ability you cancelled. Having a 3-4 second reload be restarted quickly adds up, not to mention losing an ability in a mode where you most likely will only be able to cast it once can lose you to the game. These abilities are generally stronger in damage and have lower cool-downs compared to normal CC such as a stun or root. Heroes with strong stagger abilities in my opinion:
Gammond’s silver ability: probably the most efficient and strongest non-elemental damaging ability in the game. Can hit multiple people at once (which reduces its cooldown tremendously) and interrupts any reload or ability being channeled. High damage and only gets better with gold unlocked.
Hideo’s bronze ability: An amazing pve ability at early levels, still pretty strong in pvp when used correctly. It’s a guaranteed stagger on every enemy, if you time it right you could potentially cancel more then one ability channel and reset the reload of anyone who was. Could have devastating effects that could secure you a win.
Sentry’s gold passive: A strong sentry is very deadly. His gold passive really is what makes him viable at later ranks while some people dismiss him because of his lack of power at early levels. This passive turns him from a more damage minded hero to a pretty decent utility one. With a high chance for a stagger to occur on each shot, you have the chance to chain them and prevent a hero from doing anything for maybe 7-10 seconds if you are lucky. Not to mention the flat buff to his damage he gets from it, he can also be viable to attack against his weaker elemental match up.
Keel’s gold passive: Keels’s passive doesn’t explicitly stagger enemies, but basically heals you when you do. Any hero can stagger another by simply breaking the walls the enemy is hiding behind. Keel abuses this by healing anytime cover is destroyed. Good team comps can really take advantage of her instant heal effect as it does not require a cast time, and you don’t have to use keel to trigger it. Every match you are breaking cover to get to an enemy, why not get healed for the efforts?
These are just a few strong ones in my opinion, and there is also some very strong stun and root heroes out there as well, I just see the stagger effect as the most frustrating thing to play against but also the most useful one to utilize.