Snow vs Ice?

If you don't dodge (which you probably shouldn't in raids for the most part), Ice shard deals more damage, however if you are using him as a 6th team member, the damage output shouldn't be big enough to warrant a TM (given that you have Avalanche as charged move).

They are about the same in the end damagewise but they don't work the same way. IS deals quite more damage by itself but PS charges really fast and is way easier to dodge with, if needed.

You want, Any/Avalanche on piloswine vs Zapdos.

I prefer PS because it charges Avalanche so fast, and Avalanche is a great move. But both are fine.

I used to use my double ice Piloswine a lot training up against Dragonite and I have several very solid Lapras with both Ice Shard and Frost Breath. All are very good fast moves, but I suspect that during raids the best option for a fast move is how quickly it charges. It's your charge move that's doing the damage, so the more of them that you can use before you faint, the better it is. So for raids, I suspect Powder Snow will be slightly better.

The difference is neglectible. Don't waste a tm on it.

I just used Piloswine as my 6th 'mon against Zapdos - Powder Snow & Avalanche - 1860 CP (lol). I tell you what, Avalanche was charging super quickly but what impressed me the most was his ability to absorb Zapdos' Thunderbolt. Two bolts and he was still standing!

My opinion, save your TM. PS is a fine, fine move coupled with Avalanche.