Ice Shard definitely.
I know it's tiring to keep it as a Sneasel until level 49, but even for in-game, Blizzard is a mediocre move, and horrible for a Pokemon like Weavile. Even with STAB, it has base 45 Sp. Atk. Coupled with Blizzard's 70% accuracy, it's not a good move.
What's more, Ice Shard is +1 priority as well as STAB.
If you really don't want to wait, then tutor Weavile Ice Punch instead. That's the best Ice move for Weavile, considering its stats.