Let's face it. The 2-mana slot in meta Nature decks is crowded. A little too crowded. If you want them all, that's 13 of your 30 cards!
OK, so we can't take them all. At the bottom of our list of options, we have our Skeleton Heavy and Blag Jaguar.
The Skeleton Heavy is a vanilla 2 drop Anubian for 6 stats. The Black Jag also has 6 stats with off-setting half-stat text (confused and regen) and is Wild tribe. I've been playing Black Jags for so long, I wasn't even really thinking about it. After swapping for Skeleton Heavies, I'm liking them a lot more.
Jaguar Strengths
The armor meta has calmed down a bit, but Guild Enforcers are still ubiquitous. 3 strength on the Jaguar means it can deal 2 damage to a guild enforcer instead of S.H's 1. On the other hand, 3 HP dies to a lot more creatures and spells (hello blight bomb).
The Jag's biggest strength is arguably its Wild tag. This makes it eligible for things like:
But ask yourself: are you running these cards? If you are, stick with Jaguar. The problem is the current meta isn't running these cards.
Skeleton Strengths
More HP. Canopy Barrage and Starshold bolt are the only common turn 1 and 2 removal options, and both also cost 2 mana. Burning these spells to remove a Skeleton Heavy means they aren't there to kneecap your big beasts like Moose.
No confusion. Early game is about making good trades and gaining board control. Jag's 3 Strength means nothing if it misses, which it will half the time when trying to trade (so call Jag 1.5 strength). Nature meta is also running a lot of pings.
These will make up that difference. Meanwhile, your Skeleton Heavy usually survives to trade again.
What about that Guild Enforcer? You're running these: (right?)
Your Skeleton Heavy helped you keep their board clear early game, so these hit their mark. If your Skeleton Heavy is dead, you can guarantee your Jaguar would be dead, too. On the other hand, 1 extra HP means your Heavy might still be alive. If so, all you need is that 2 damage to finish the Enforcer after a Canopy Barrage.
Where else does Skeleton Heavy excel? Buffs. Any buffs, really, but especially frenzy buffs:
These don't play so well with confused creatures. These buffs are best in decks where you can guarantee face when you need to. Buffs in general are like this. You're investing more mana into your creatures. It's important that you can reliably make the most of it.
Core Set Refresh
This will change things a bit. Amazon and Wild deck types are being supported in more ways. For example, Wild Staff will only proc root if you have a wild creature. There are several other things like this, but in short, Wild nature decks looking to get wide will be coming back. If that is your deck, Jag is back in. Until then, it's just being edged out.
Edit: 
Conclusion
I started realizing that during the mulligan phase, I would always toss Black Jags back. Why? It's a two-drop and should be a good keep. This got me thinking and ultimately led to me dropping them from my decks and writing this post. If you think I've missed something that keeps Jags on top, please let me know!