Tanks: HP or DEF champs: give them lots of hp and def

Nukers: crit damage

asking for a friend  but.......

any suggestions of specic gear sets  for said types  of champions?

Well stats over sets, meaning that you worry about hitting good numbers first and foremost and sets are like a distant third. 

However in general, if stats are close to equal, nukers love to have sets like Savage, Lethal and Instinct to cut through opponents defense and deal way more damage.

Tanks are often fans of Stoneskin, especially if you use them in arena. There's also sets like Bolster for shields and heal, or Regen and Immortal for some bonus heal.

Champs that apply debuffs or remove buffs as part of their kits just love Perception, still one of the best sets in the game. And the new Feral set. Those can be used as filler sets to get some bonus accuracy and speed. 

Big AoE nukers love Slayer, that set is easy to find good builds for with all the set bonuses leaning hard into damage stats.

Ofc these are just a few, and this is all dependent on the builds being good in those sets. Like if the best you can do is 3k attack 65% CR and 111CD in a Slayer set, better to build the 6k attack, 100CR, 265CD version with no sets.