Hey there Juulz85:
I can't speak to conditions for expert skiers, since I'm intermediate, but having just come back from Banff last week, I can offer my observations about the towns and the slopes.
It was common knowledge among the people I talked to that Sunshine Village had better snow, but my experience was that it really depends. I encountered spring conditions on the front face of Sunshine one day, and it had been snowing the day before at Lake Louise.
As far as where to live, if you're young and want a night scene, Banff is definitely your top choice. It's very touristy, but there were tons of younger people there. Or you might want to consider Canmore, which is where I stayed. It's a 10-15 minute drive from Banff, less populated, but still fun and very funky.
Also, as someone else suggested, be sure to consider working at Norquay. I didn't ski there, but it's the closer to Banff than either Sunshine or Lake Louise.