It's very likely to be Articuno, Victreebel is legit too. Everything else listed is just behind with Moltres being decent. Persian has some chance too.
It's weird that Articuno and Victreebel aren't ranked at the same level, as they have always been, but a little bit more than half guys decided to promote Bel and little less than half decided to not do the same with Articuno.
The main difference between Articuno and Victreebel is that Articuno does very well against Tauros, Snorlax and Exeggutor; it can be splashed on a standard team, while Victreebel is a doublet of Exeggutor and asks for a specific build (lead + 3 normals + Bel +a filler just like Starmie is an option too).
Victreebel has that combination of Sleep and OHKOs on GolDon + para'd Starmie, and greedy options like Wrap and Swords Dance - it's higher risk higher reward, and that reward is something I have always struggled pulling off, especially after Body Slam tragedy.