I would say that best beach for snorkeling in Ibiza Town is Playa Figuretas, because of its location and calm water.
But there are beaches with much clearer water outside Ibiza Town.
For example:
- Cala Salada - Near San Antonio
- Cala Bassa - Near San Antonio
- Cala Conta - Near San Antonio
- Playa Cavallet - Near Ibiza Town, in Ses Salines natural park (this is nudist beach)
- Ses Illetes - Is in Formentera (does worth it, the best beach I have seen)