Decide what apres actually means to you before you book, because the word covers two very different nights. If you want to dance on a table in ski boots while the sun is still up and keep going until 2am, Verbier is the answer and Saas Fee, Laax and the Jakobshorn side of Davos are the chasers. If apres means a beautiful terrace, a good bottle and an early dinner, St Moritz, Crans Montana and Grindelwald serve that far better and you will hate the noise of the party towns.
Then be honest about the budget, because Switzerland is the most expensive place to drink in the Alps. A wild week in Verbier or Zermatt with bars, clubs and slopeside rounds belongs firmly in the $4,000 to $8,000 per person band once flights and beds are in. You can pull the same trip into the $2,000 to $4,000 band by basing in Nendaz for the 4 Vallees, in Saas Fee for student prices, or in workaday Davos rather than a glamour village, and skiing over to the famous scenes for one big night rather than every night.
Match the resort to the group too. Powder skiers who party will be happiest in Verbier, Engelberg or Laax where the terrain backs up the night. A mixed group of skiers and non skiers does better in Zermatt or Grindelwald, where the views, the walking and the variety keep everyone happy. For the wider picture see our apres ski across the Alps ranking and the best apres ski resorts in Europe, then read up on the country in the Switzerland destination guide.