I've seen all the shounen and HxH is my favorite for multiple reasons:
the characters:
In many shows we have the protagonist and all the other characters are kind of like his side dish. In HxH Kurapika, Killua and Leorio all have lives on their own and aren't dependent on Gon. What i also enjoy is that Gon isn't the chosen one who's 100% good and can never fuck up, he's just a brat with insane potential and makes quite often mistakes. You just have to notice that Togashi treates all of his characters with respect and doesn't prefer some over others, if you understand what i mean. The villains are probably my favorite part of the show.
The plot
It's unpredictable, but at the same time there are never asspulls, and every arc is vastly different from the others. For example i enjoyed One Piece when i was younger but for me it's now incredibly stale and repetitive. There are never any consequences or character development, just rinse and repeat. The plot develops organically, you rarely have the feeling that Togashi pulls the strings.
The Tone
Even though HxH can be really funny, sad or brutal, those emotions don't clash with each other. If you have a sad or badass scene, it won't get ruined with stupid humor(like in FMA:B, still a great show though)
Flashbacks
In many shounen you have dozens of flashbacks, every character gets one, and everyone and his mother has a generic tragic past, which is really cheap imo. Also these work against character development, they basically confirm that the character will never change. In HxH flashbacks are used with reason, and most of them doesn't show a tragic past.
Nen System
Self-explanatory, i don't have to explain why it's the best anime fighting system. The fights are amazingly tactical, after i've finished HxH other fights seemed just so bland. You may have good choreographies but they still don't make sense, like the characters don't even want to win, they wan't to put on a show for the viewer. In HxH most fights are short and not unnecessarily drawn out.
Dialogue
I really enjoy the dialogue, and on some scenes like Pitou's ambush, Netero vs Pitou or Netero vs Meruem, you really have the feeling that every single sentence, every single word has a purpose and is just perfect.
Shounen Tropes
Most of the generic stuff from other shows is missing. You don't have a pointless big-breasted bimbo following the group for fanservice, the message of friendship is shown rather than just slapped on, it isn't repetitive and stuffed with filler. No huge and flashy abilites, or "justice porn", in short, it's never cheap. There are many subversions of common tropes or very unusual plot developments, but even the people who don't know about them can appreciaty HxH for different reasons. I know no other anime where the entire first page of MAL reviews are 10/10's, and that's amazing imo because HxH never tries to appeal to everyone, especially during the CA arc, but it always works on multuple levels, so someone doesn't enjoy one aspect, there's still something else to get excited about.