What is The current most OP support in your Opnion?

Easily Ana -- at least from about diamond up. Her heals is the highest heals per second of any healer, outside ultimates, with the only two downsides being that you can miss some shots, and you can't heal through shields. Her DPS is also very high for supports, second to only Zenyatta, meaning that combined with the rest of her kit, a good Ana should be able to confidently duel any hero in the game. Her biotic nade is very powerful in boosting heals by 50% for teammates, and providing an instant heal of 80 to bail teammates out. Where this ability's true power is, though, is in its ability to deny healing for enemies. Any anti-naded enemy will be easily focused down and killed, and it is the only counter to transcendence, and any high healing comps to stop them dead in their tracks. Her sleep dart can put any enemy out of the fight for 5.5 seconds, which will usually be enough time to get one or two picks for your team and secure the team fight victory. Her nano boost is incredibly valuable for saving teammates in a pinch , and turning a situation where they would die into a situation where they can now go in and kill the whole enemy team. It also pairs very well with tanks like Winston, Dva, and Reinheardt, and with DPS such as Genji and Reaper to wipe out an entire team with just two ultimates.
I would say that a close second is Zenyatta with his DPS rivalling the highest damage DPS heroes, discord orb basically taking a third off of any character's health pool, a realiable zero-cooldown healing ability, and what is arguably the best ultimate in the game.
For lower ranks, Moira is very powerful for her raw healing output, and her easy intuitive nature. Paired with her life steal and fade, many teams at lower ranks simply won't be able to focus down and kill a Moira in most cases.
Hope this helped.