I;m more about who plays best in pug v pug because prem is a different ball game and one i don't experience too much.
Horde:
Hunter: Krimal (awareness, CC, repicks)
Rogue: Ivxnl (beast) or Pacov (extremely intelligent gameplay)
Warrior: Swag (by far best pug always trying hard)
Shaman: Partytoilet (support, objective, totems, positioning. Guy knows)
Warlock: Zibro (sleeper who prob no one has heard of but the guy knows what's going on: CoT, soulstones, fears, nades, etc.)
Mage: Meechy (popping consumes when absolutely necessary,going for wins even with shit teams, polys over frostbolts, detect magic spam)
Druid: Wsgstar (elevated play)
Priest: Yezriel or Contagious (clutch MCs, timed fearbombs, dank flag carries, good scouting, etc.)
Alliance:
Hunter: Ednaryt/Demonhunter/Iacopo (One of the best. Stellar and original gameplay on the regular) Sarei (great instincts and amazing meta)
Rogue: Acely (amazing all around play: fcing, defence, offence, support, etc. Great consume use/trinket use. God-like reflexes) Heartstabber (Great consume use, really good scouting and team direction, fantastic desire to win and try harding, team player)
Warrior: Ochs (great support, positioning, timing, macros (weapon switch/armourswitch), going for obejctives) Enthrall (all around beast, great awareness), Vymi (really good instincts, always playing to win, team player), night elf fem war from <not like this> can't remember your name (really nice use of shadowmeld, intellegent use of cooldowns, playing to win, good weapon swaps), lots of nice ally wars. Honourable mentions: Tfwnowf (amazing repicks and great macros (sword and board to shieldwall), Arb (sick positioning and objective, great shadowmelds and amazing reflexes)
Pally: Functiion (always trying hard and going for objectives, great support), Arinoa (beastly ret pala, will make you suffer for misplays), Icairus (all around best pally: engi use, objective, support, damage, fake casts, etc.)
Warlock: Edhris (great positioning, instincts, spell use (CoT, Hellfire, trash buffs, shadow ward, etc.), engi use, support), Cooplock (beastly damage), Vancocin (all around best warlock, can do anything with expertise), Djfresh (big respect for the tryharding: always on objective trying to win games)
Mage: Alwaysrussia (number 1 support mage in game, unreal instincts, very conservative (positive) gameplay), Snille (great all around gameplay ( carry, support, kill efc, peel, CC, etc.), Tank (great burst and defence, always on objective), Danielle (fantastic FCing, one of the best) Cvika (underrated but will absolutely make you pay for any mispplay), Kupcha (always trying hard, going for objective)
Druid: Scratch (always trying hard and helping out), Zomgabomga (always going ftw), Bioniclass (showing how other specs can be more than just novelties)
Priest: Grundlesnax (fucking carrying games: dispels, engi, positioning, objective. Guy is on point)