Maestro certainly has one of the best defense, with a 35 damage and a fairly less recoil and an 80 round mag capacity. Also, with Buck losing his grenade it becomes even more difficult to defeat Maestro with him being bulletproof. He can deny bomb plants, gather intel, and deals with significant damage with a superior defense gun, which makes him a must-have op.
Another defender, well known for its loadout. He can use the shotgun to open hatches and other holes. Also, the secondary SMG is as good as primary. The plant denial gadget and the recently buffed shield generates large possibilities on any map.
Jager even after being nerfed is a really nice choice as being a two armor operator, as now he can take more damage. Also, he has the best guns on the defenders' side. He can also completely get rid of all the incoming projectiles with just a grenade.
Thermite being the first wall breacher of the game, he does it all for you. Opening up hatches, walls and taking anybody down with among the best ARs of the game. Thermite is also among the strongest operators of the game.
Thatcher has to be on the list as it is a good match for Thermite. Thermite and Thatcher are amongst the most powerful duo of the game. Even after being such an old Rainbow six siege operators duo, it is still highly functional. He has the ability to destroy bandit batteries, mines, and destroy almost any defensive setup.
These top 5 rainbow six siege operators are primarily useful for above diamond level competitive gameplay. Now go try them out yourself and let me know in the comments below if you disagree with the choice!