Balanced Hackmons is a ton of fun! It's still pretty new, so there is a ton of things to explore!
I've seen various different sets in Hackmons lately. Simple Quiver Dance Mewtwo, No Guard Inferno and Zap Cannon Mewtwo, PerishTrap Giratina, U-turn Slaking -- a ton of different things. It seems like every few days the meta changes; however, there are a few threats who have pretty consistent use in Hackmons.
Deoxys-S, Slaking, Giratina, Shedinja, and Groudon. (Although Shedinja and Groudon's usage has been a lot lower lately for some reason.) All of these are very common in Hackmons. Deoxys-S will usually be a lead, Slaking will usually be a crazy powerful attacker, Giratina can be doing many different roles, Shedinja can totally destroy a team once certain things are removed thanks to Sturdy, and Groudon is just plain bulky and has great attack.
Slaking is, in my opinion, the best Pokemon in Hackmons right now. 160 base Attack + Pure Power allows it to 2HKO so much in Hackmons and it can revenge most set-up sweepers as well. It's just incredibly powerful, and it can also tank many attacks as well. Regigias is also great; only problem is Hackmons tends to be more physically oriented thanks to Pure Power so Regigias higher Special Defense niche is a lot less useful most of the time than the higher Defense that Slaking has.
Anyways, like I've said earlier, Hackmons is a pretty crazy tier at the moment. I've been seeing a ton of different playstyles lately, such as BP and weather teams. All of them tend to have significant flaws, so I'm interested to see how people improve these kinds of teams. I'd also like to see more leads! Pretty much every lead in Hackmons is Deoxys-S or Jirachi. I'm sure there are other great options out there!