I'm heading to Malia in early August next summer, and I've heard the Malia strip is slightly bigger than the Zante strip. Sunny Beach isn't too popular yet and isn't all that safe, so I'd give that a miss. Kavos is meant to be awful - dirty beach and a constant lingering smell in the air. Magaluf is probably the safest, but also the busiest and can be quite expensive. I'd recommend Malia or Zante, to be honest.