If you're buying expensive ones, I would make sure the lenses are very good. Not average ones like in most designer sunnies. Maui Jim, or Serengeti have great lenses. Lovely to wear.
If the lenses don't bother you much, I'd buy cheap fashionable ones. Expensive ones are a nightmare to watch, you'll sit on them, or the kids will tear a leg off them, or you'll scratch them, or you'll leave them on a store counter and remember a week later. Obviously I wouldn't do any of those things. But I believe these things easily happen.