For that meta, I would rate them as such:
Teeg is fairly useless as a commander here, as most stax and counter cards are under 4 CMC; he won't be shutting down much. Thrun is a good beater who can resolve himself, but until you find Rancor / equipment, Talrand will chump block with Drakes all day. You could run City of Solitude or Dosan to make up for that, but still, it'd take a while.
Sisay, as you said, can fetch up cards to keep your opponents at bay. Fetching Dragonlord Dromoka or resolving Grand Abolisher first would keep you safe from Talrand for at least a turn, and dropping Elesh Norn after will slow him down considerably. She can also find Dosan if need be, has access to spells to destroy GAAIV's trinkets, and can ramp past his tax. Of course, they can just hold down Sisay and slow the deck down considerably, but whatever.
Ruric Thar is ranked so highly primarily because neither GAAIV nor Talrand pack their decks with creatures, so he's a wincon for as long as you can protect him. The fact that he's forced to attack is negligible; you can run Maze of Ith if you're afraid of him connecting, and if I recall correctly, he can't be forced to attack into tax effects like Ghostly Prison. You can choose not to pay, which would prevent Ruric Thar from swinging. If he resolves, then someone has to take 6 damage to remove him. You can use fight mechanics to kill off GAAIV and Talrand, still have access to ramp, have access to Fork spells in case of emergency, and can run cards like Price of Glory to make their spellslinging even rougher. The drawback is that both Talrand and GAAIV can resolve before Ruric Thar, making it more difficult for him to safely resolve. If it's too difficult to land him, remember that you have access to cards like Guttural Response, Red Elemental Blast, and Vexing Shusher to safely resolve him.
Teferi was listed as number 1 because, as you say, shutting down enemy counterspells completely is a godsend. Once their greatest weapons are gone, you can do whatever you want. He won't stop GAAIV's taxes, but you can probably work around that.