we went to Jasper Canada last March and it was fab, looking on the webcam this week there is plenty of snow and blue skies!! www.skimarmot.com
looking forward to Bansko this year though as not a lot of nightlife in Jasper!
We're going to Banff, Canada next saturday and there's been 10ft of snow so far this season. They have guaranteed snow every year and they also have a long season, running from mid November to early May. You can't really go wrong if u pick there. Lake Louise and especially Sunshine Village, have the best snowfall records in Canada. It is very cold though, today it's forecast at -51 at the top of the mountain in sunshine village!! That is with windchill though.
Whistler is always a good bet, and anywhere else in Canada can be generally relied. In Europe aim at somewhere with a glacier- Les Deux Alpe, Zermatt, Hintertux, or somewhere very high - Chamonix, Val Thorens spring to mind.
However, just bare in mind that weather, and particulally mountain weather, is very unpredictable, and nothing is ever guarenteed!
Worldwide? I'd go for Alyeska Alaska, Riksgransen Sweden or one of the Japanese resorts. None of those are cheap or in most brochures mind...
As Steve said the best bet is to go somewhere with a glacier, we did this last New Year (Passo Tonale, which was small but fun)