Destiny - Iron Banner giving context to your accumulated power and weapons, armour etc
Trials for that 3V3 intense, no respawn, risk / reward for revives and great loot. One loss can be devastating.
Rift for that more sport / team work dependant style of play.
Mayhem for supers flying all over the place.
Combined arms for big maps and vehicles.

Rocket league.

Call of Duty: Black Ops 3

If we exclude PC games, I'd say Smash for Wii U. It's my personal favorite and the competitive scene is doing very well since they had 1,926 entrants for Evo 2015.

It's soon going to be replaced by Street Fighter V though if we suppose the Ultra Street Fighter IV competitive players will move on to SFV once it is released.

Rocket League easy. I have a hard time believing that anyone who says otherwise has played it.

Interesting, the OP question got like 15 different "obvious" replies :)

Well, I haven't played so many but Splatoon is amazing, Titanfall is the most fluid experience I've had in multiplayer but Halo 5 is the greatest multiplayer I've ever experienced. Having never been a huge fan of it, I've now poured hours upon hours into Warzone, Breakout and Swat. The level design is so thoughtful and the intensity of Warzone is unlike anything I've tried before. So Halo 5.

Titanfall thread? Titanfall thread.

I'm in agreance. Despite the fact the game has barely any players left I'm loving it. I just wish I could play the other modes, only attrition really has anyone left 

^ this. Even tho i stopped playing lol long time ago, still love to see TSM get rekt by others, lol (no offense to TSM fans). One thing dat i don't like about LOL is just dat the Korean are TOO DAMN OP! This year World Championship grand final is pretty much Korean v. Korean...

Oh and btw, In term of prize pools I'm pretty sure Dota 2 take the cake. The game is also very fun to watch as well. :).

What platform you play on? I know on PC it's been dead for awhile due to Origin and other games being extremely more popular, but on Xbone I never have trouble getting into a game. I almost only play Last Titan Standing which is the 4th or 5th most popular mode and it's still easy to find full games. Idk about 360.

I'm gonna get back into it between Fallout 4 sessions and try to get that god damn Killed Them All achievement in other modes.