My thoughts ...
1) Buff heroes are now trash (except C'tun due to Whelp Smuggler effect).
2) The best heroes despite what HSReplay says are probably Janice Barov, Silas Darkmoon, Reno Jackson, Flurgal. Silas can do 10 discovers a game. Reno just needs one "win the game" unit to make golden and potentially run away with the game. Flurgal is out of control good.
Win The Game Units:
1) Impatient Doomsayer
2) Whelp Smuggler
3) Tarecgosa - the 4/4 dragon that keeps all combat buffs. Divine shield from Selfless Hero or Nadina is a buff. Crazy strong.
4) Dazzling Lightspawn - if you are going elementals, never get rid of even one of these.
5) Insatiable Ur'zul - the Tier 5 demon that eats Tavern minions itself. You can get this to 100 health rather quickly with Impatient Doomsayer synergy.
6) Bigfernal - Tier 4 growing demon, synergy with Impatient Doomsayer.
For me, I can't quite see a way to make Beasts consistently work, but Illidan can do it. Monsterous McCall and Leapfrogger plus Rivendare is so strong. Pirates are hard to pull off, seems that the pirates really needed to win games are Tier 4 and higher -- I've seen some players use Reno Jackson on Tony Two-Tusk and create nightmarish Pirate boards. Mechs can win, Holy Mecheral is great and Omega Buster is a broken strong Tier 6.
I don't see any Quillboar boards in the late game.
Master Nyugen is really good and really strong and quite fun, but he isn't quite the best hero. Depending on what tribes are in the game, Jandice Barov's ability to manufacture triples multiple times or how Silas Darkmoon can both board flood and do countless discovers are better. If murlocs are in the game, Flurgal is broken.
I dont care what HSReplay says. There are 2 very broken heroes in game. Shudderwock with tokens is almost always autowin. Nguen is broken as hell. Noone in their right mind will pick Silas or Flurgal over it.
Leapfrogger is just broken. Lvl 2 minion that is played over T6 Wolf is just stupid. Also the animations...
My suggestion to fix: remove shudderwock,
make Nguen random , not pick one,
Leapfrogger cant buff minion that already has this dearhrattle.
Impatient Doomsayer: Avenge(4)
And buff pirates.