Firstly some basics: An island is a free standing structure, offering an all round access, whereas a peninsula is essentially an extension of your kitchen, being attached to a wall and offering three open sides.
Islands and peninsulas both offer great benefits and are highly functional. From creating extra work surface, additional storage and more room for socialising with your favourite people! Although the decision making process between the two may seem daunting at first, in reality it’ll more than likely come down to two major factors: the shape and size of your kitchen & livability (In other words, how do you and your family function within a kitchen and how will that be affected by the structure.)