ohmigosh, you guys have replied to each other so much, I dunno which one to reply to anymore.
Juniper is still the best supporter, that's it. Oh you have to discard a M blastoise? too bad, you'll have more, and it's not even that great of a card.
The only decks that really really really don't benefit from it that well, are usually bad decks, or decks that CANNOT replace their resources, at all.
Darkrai(or all the new shtuffs) Blastoise and Emboar are three EXCELLENT DECKS, that NEED juniper, why? because refreshing your hand to 5 rather than drawing 7 new ones is weak, especially since in Darkrai, you need to discard energy to power your pokemon. In both Emboar and Blastoise, you should run juniper over Shauna, as well as running superior energy retrievals (or basic ones, whichever fits you) so that you can easily power up, quicker and more efficiently. You can also discard cards that you don't need, or just can't use, and just get rid of them.
Shauna is average, It's just so basic, 5 cards is fine, with Juniper, you get 2 more, which is 2 more chances to get a good hand.
That said, I like Shauna, it's good in some circumstances, but Shauna is not better than Juniper, under most circumstances, you will run more Juniper than Shauna, and if you need to run Shauna, you'll probably run Juniper as well.
I run 4 Juniper and 2 Shauna in both my Darkrai Yveltal deck and my fairy transfer deck.
I run 4 Juniper in Emboar, and everyone at my league are running Juniper over Shauna in their Blastoise decks (I also had one, where I ran 4 juniper, but blastoise is boring)
I run 4 Juniper in VirGen and 3 in Empoleon (Empoleon is a deck that can split evenly on Shauna vs Juniper, because not only is it a shuffle supporter, it's also necessary to not loose your Empoleon lines.)