Always Wild Growth - without exception.
Against Mage and Shaman you really want Wrath; you need to get rid of the inevitable early Mana Wyrm or Tunnel Trogg. Feral Rage is also quite important for Flamewaker and Totem Golem removal; or Swipe with Wild Growth (or the coin) as you can use it on turn 3 if required.
Only keep Nourish if you've got Innervate; gaining 2 mana on turn 3 can be incredibly useful - this deck is definitely top heavy.
Bloodmage Thalnos is a great lure against aggro. Early game it might buy you a turn (ideally remove 1 durability from a weapon while its at it) and get you a card draw.
Druid of the Claw seems expensive to mulligan for... but it's basically the cheapest disposable minion in the deck! And it can have Taunt. Turn 3 with Innervate isn't bad.
Odds are, against Control, you're going to need some hard removal which this deck lacks... just hope against hope for Mulch or Naturalize from your Raven Idol. Otherwise Northshire Cleric > PWS > Kabal Talonpriest (then Inner Fire for the final insult) is the kind of thing that's just going to result in "I concede to you".
I found 2 Gadgetzan Auctioneer much more reliable than one – and it’s virtually a Taunt creature, nobody will let it survive more than one turn; you don’t need absolutely masses of card draw from one as there’s always the other. Essentially they enable you to drop both Arcane Giant very cheaply.
If playing against Renolock or Paladin the Arcane Giants are lures as much as anything else; you (really, really) don’t want to get hit with Twisting Nether or Equality > Consecration just after you’ve dropped Aviana, Kun, Malygos and Ragnaros all on the board at once…
The biggest problem is holding it together in the early game – especially against aggro. You need to suck up some early damage in order to ramp as hard as you can; if you can get the mana then the card draw rolling, you’re laughing.