I was playing some mediocre decks and fell into dumpster ranks (around 4000), it was really frustrating getting fucked by mages so i decided to search for the best mage counter and i found this hunter deck on HSReplay. I think this is the most optimal list, i wouldn't change a single card. It's amazing against mage (18-6) and paladin (11-4), after the nerfs there should be more warlocks around and this deck seems good against them aswell (5-0), the worst matchup is priest (0-4) and the games weren't close, priests absolutely obliterate this deck.
Update: just played 10 more games and won every single one, the deck is extremely consistent, not sure why we don't see more hunters on ladder.
Mulligan: always keep Intrepid Initiate, Imprisoned Felmaw, Adorable Infestation, Wolpertinger and Demon Companion. Scavenger's Ingenuity is a very good card and i usually keep it but if i'm playing against mage without coin and i don't have a 1 drop i would skip it, it's crucial to put pressure from turn 1. Sometimes i would keep Headhunter's Hatchet (if i have Wolpertinger+another 1 drop). Sometimes i keep Rinling's Rifle (if i am playing against paladin/rogue and already have a good opener). Also sometimes i keep Tour Guide and Wound Prey (if i have Adorable Infestation or to activate Intrepid Initiate effect). Never keep Quick Shot, Tracking and remaining cards which are not in the list above.
Some tips: against mage always keep in mind secrets they might play next turn and try to create a perfect situation where neither Ice Barrier or Counterspell will prevent lethal (for example you might want to save Tracking if you have 1-1 and Piercing Shot in hand to play around Counterspell), same goes for Oh My Yogg!. Also sometimes you should hold on to your spells to play around Netherwind Portal (they have a lot of burst damage and an early 4 drop might connect few times to face and mage will race you faster because of it) or if you have two 1-1s you might want to play around Ice Barrier and not attack face (assuming you put opponent's health low enough already) and usually i don't play Trampling Rhino on the empty board, i would rather play 1 drop and press extra hero power. Of course these tips are situational and you shouldn't always play like that, take your time, analyse your hand and play according to what you have. Have fun!