ZH/HS better than ZH/HB in real world battles?

Not really. HS doesn't hit Dragonite or Machamp as hard as HB, and the gym AI doesn't use multi-bar moves nearly as much as it should.
HB is also more likely to trigger the faint-revive loop, and hits much harder if you miss a dodge, so is better overall, at least until the gym bugs are fixed.

I would rather take heavy slam.
2 and 3 bar moves makes battles more annoying, cus opponent have to dodge more.

Also if opponent have big cooldown charge move, then they are vulnerable for second heavy slam if snorlax decides spam it twice in row.

(There are only few 1 bar moves that i fear in battles, hydro pump is one of them, it hits very fast these days.
Very annoying to dodge)

It depends who is attacking the gym. If I don't know the moveset beforehand, I'll use a Tyranitar. Tyranitar resists BS and HB, but HS is super effective; so HS is the most troubling charge move for me.

However, if didn't have any decent rares, I'd probably choose a Vaporeon, In this case, HS would likely be the least troubling charge move since it is resisted, lacks STAB, and relatively easy to dodge with the short duration WG.

Against a ZH snorlax, I usually use machamp or heracross so I'm dodging every move. Since I'm dodging every ZH, HS is pretty easy to dodge. I take less damage from the HS variety as a dodged hyper beam still does a lot of damage while a dodged heavy slam does minimal damage.

HS is resisted by Vaporeon and Flareon though, two most common generalists often used to fight Snorlax.

I pick Heavy Slam. Because I have battled both and have a little ensi wensi difference in challenge.