While i agree Skala is a great resort, for teenagers it may just be a little on the quiet side, especially if you are not hiring a car as public transport down in Skala is virtually non existant.
Lassi may well be a better option as it is more centrally placed with the capital Argostoli just a stones throw away.
Lassi is not a personal favourite of mine but it gives you a few more options for seeing things if you are not hiring a car. If however, you are taking in a few excursions such as the island tour, then i would definately say SKALA!