I’m local to the area and familiar with both sites. Weekends are crowded, especially Devil’s Den. Blue grotto caters strictly to divers and thus not so crowded and is technically a more challenging dive. Both equally have their charms and recommend a 3 mil wetsuit and light. If you can swing a weekday visit (Tues-Thur) its a more pleasent experience. That said, message me and possibly can make it happen. PADI Rescue Cert