Hearthpwn

I hit legend pretty early in the season with midrange shaman, and i think it's actually much better in wild than in standard.

According to Tempostorm, the top 4 decks in wild are secret pally, zoo, midhunter, and patron warrior. All of these are aggro/midrange decks, but don't have any good ways to come back after a Lightning Storm or Maelstrom Portal. Nzoth isn't a problem if you can hex Savannah Highmane or Sylvanas Windrunner or Tirion Fordring or whatever, and the rest can be easily cleared with spell damage boosted aoe. 

The only really bad matchup for me was freeze mage (probably 25% winrate) because Eater of Secrets doesn't automatically win you the game if you haven't dealt enough damage or have no room to play him. Nzoth Priest isn't that bad honestly, as long as you don't play into their board clears, but it is probably slightly unfavored. 

Honestly, the only non-control deck I've played that was favored against Shaman was Midrange Hunter (Before Call of the Wild Nerf) because you could actually win the early game with Mad Scientist+ Freezing Trap/Snipe, clear their board with a Knife Juggler and Unleash the Hounds combo, and finish them off with Call of the Wild before you go into topdeck mode.

I was in your position only a few months ago. I crafted both Sylvanas and Thalnos, and I've gotten much more consistent use out of Sylvanas. Thalnos is currently played in Shaman decks, Rogue decks, and Freeze mage, while Sylvanas is mainly put into Control decks, but can also be put into most midrange decks. The thing about Thalnos is that he is only useful in a few archetypes, and can be replaced more easily than Sylvanas in most decks he is played in. Sylvanas, on the other hand, is basically an irreplaceable card in Control Priest, Control Warrior, and Nzoth decks. Control Warrior + Priest are probably going to be around forever, while Shaman is more or less dead after TGT and LOE rotate out (No Thunder Bluff Valiant, Tunnel Trogg, Totem Golem, Tuskar Totemic). Freeze Mage will probably be a deck forever too, but its really bad on ladder right now with so many warriors, and Miracle Rogue is dead against the Shamans and Zoo on ladder. Control is kinda bad too, but Sylvanas can be good in basically any deck while Thalnos is more specific. I wouldn't craft Thalnos unless your sure you want to only play the decks he's good in.