They're very different hotels, so hard to directly compare. The W (assuming you're not getting and hiding away in a Villa) is quite a loud hotel full of 20 and 30-somethings who are not always the most civilised. It's fun, quirky and has a vibrant evening scene as well as being close to Potato Head and its well regarded lounge. The Sunday brunch is a legendary boozy affair (though I found it slightly tacky compared to expectations). VB is more what you'd think of as a honeymooner setup, with some really gorgeous rooms and a peaceful vibe. Personally, I'd do VB, but partially because I greatly prefer Thailand (even Koh Samui) over Bali.