Currently?
Probably Magi or Gintama. There's also HunterXHunter (if you consider that "ongoing" tbvh troll streak too OP).
Also don't be too quick to judging shonen based on the few bad mainstream titles.
What about Akame Ga Kill? I saw an episode of it on Toonami and it looked pretty awesome. What's wrong with it?
Okay then...
1. HxH
* 2. Toriko
3. Magi
* Note that Toriko doesn't attempt character development but when it does it's good. That being said it could use character development with it's main cast. Magi is much better in that regard. However, I placed Toriko above Magi since it's world is far better than Magi's and has a cool backstory to it with great foreshadowing tied into it. I personally, like the fights more in Toriko than Magi. The artwork isn't that amazing in Magi IMO.
Main manga or Zero? Cause zero might be seinen if I remmeber correctly
But yeah anyway no, Imo akame ga kills characters lack depth and panel time, plus the plot and the characters seemed forcefully shaped in a way convenient for the MC that one could literally telll who would die next and for what reason. I ultimately dropped it.
This being said, there were some well developed characters like lubbock,Najeda esdeath, Izou etc....akame herself was decent but again prettty one dimensional. It also seems like the manga will end just exactlylike the anime (which was so shitty that I couldn't stop skipping the last 3 episodes or so)
All this is just my opinion, go check it for yourself I'd suggest
So basically the best 3 have major flaws that prevent them from being completely recommendable.
Hunter x Hunter: author isn't committed to the weekly schedule often taking long breaks
Toriko: very silly premise and unsophisticated characters
Magi: uninteresting world and mediocre artwork
Okay then...
1. HxH
* 2. Toriko
3. Magi
* Note that Toriko doesn't attempt character development but when it does it's good. That being said it could use character development with it's main cast. Magi is much better in that regard. However, I placed Toriko above Magi since it's world is far better than Magi's and has a cool backstory to it with great foreshadowing tied into it. I personally, like the fights more in Toriko than Magi. The artwork isn't that amazing in Magi IMO.
I'm surprised you did not mention Jojo.