Antigua is low, dry and ringed with coves, and the local line is that it has 365 beaches, one for each day. The coastline is so indented that even busy weeks leave empty sand somewhere. It is also a serious sailing island, with English Harbour at its heart.
We usually split a week between two sides. The west coast has calm water and sunsets; the south around English Harbour has Nelson's Dockyard, restaurants in old naval buildings and the Sunday view from Shirley Heights. A day on Barbuda, Antigua's quiet sister island, is the other essential.
The honest caveat is that inland Antigua is scrubby rather than lush. If you want rainforest and mountains, St Lucia is the better choice. Come here for water, sand and boats.