As a defender? Potentially, but not likely. Say that Togekiss did have Fairy Wind, it's viability as a defensive move would depend entirely on how the move functions. If it's a big slow move like Confusion, then it would be great on defense. If it's a weak but fast move like Dragon Breath, then it would be garbage on defense.
On top of that, Hidden Power both packs a punch and can offer up an element of surprise to attackers. If you're aiming to raise a Togekiss for gym defense, cross your fingers that you get Hidden Power: Ground, as it hits for SE damage into a ton of Togekiss's counters. If you end up with a less-desireable Hidden Power, you can always TM to Air Slash and call it a day.
As for what you should use your Sinnoh Stone on, my advice is that unless you have a gap in your lineup that one of these new Mons could fill, go with your gut and don't second-guess yourself. Roserade, Electivire, and Weavile are all top-contenders for their types, which is why they tend to be popular choices. That said, none of them are essential right now either.
TL;DR if your first gut reaction is to evolve a Togekiss, then go for it! That was my choice, and I have zero regrets about it.
