We had a very nice stay at the Hotel Marelba! The staff was very friendly and at least one of the them spoke very good English. Our room was with a perfect view to the inner court yard, with beautiful palm trees! The room was clean and simple, just enough for us for a perfect holiday on Elba!
Cavo was a nice small town, with nice restaurants and the time we stayed there, it had even a small festival to amuse us.
We recommend the hotel and Cavo for easy travelling. It is easy to reach from Piombino by ferry- which can be a chaos, but "that's Italian"!
For visiting nice snorkelling beaches, we had a car because even though Cavos beach was nice, we wanted smaller beaches with more cliffs to look at!