I think that Hail Teams usually fail since it only allows one thing to benefit from it - Blizzard. Although it's worth it, having a 120 Base Power Attack at 100 Accuracy with a chance of Freeze status, it's only one factor that benefits from Hail. The immunity to be damaged by Hail is also another factor, a little, however. You can use EnduRev/Endure+Flail or Endure+Berry Boost in Sandstorm by most Pokemon, since most of them are immune to the Sandstorm damage, such as Lucario and Kabutops, but non can in Hail, except Glaceon if you use it for Flail. The SpD boost in Sandstorm for Rock types make Sandstorm get more attention than Hail teams as well.
There are more offensive choices in Sandstorm teams. Garchomp, SD-Gliscor, Tyranitar, Lucario, Nidoking, Rhyperior, etc. Nevertheless, there is an improvement for Starmie and Porygon-Z, where they gain better Ice type moves, and Walrein.
If it's based on usability, I'll definitely lean towards Sandstorm teams as they gain many options in terms of offense and defense, while Hail Teams lack the defensive side. If it's based on 'whether-you-prefer-to-use-[Insert Team Here]-just-for-fun', I'd go with Hail since you get to use 120 Base Power Blizzard. >:] The bottom line is, Sandstorm beats Hail teams hands down, but Hail teams are not useless.