Five penguin species breed there: gentoo, king, Magellanic, southern rockhopper and macaroni. Gentoos, Magellanics and rockhoppers are the highlights on most wildlife itineraries. The Falklands are the one destination on a polar route where rockhoppers and Magellanics are a realistic expectation rather than a fluke.
Beyond penguins: black-browed albatross, southern giant petrel, striated caracara, steamer duck, geese, cormorants, shorebirds, South American fur seal, southern elephant seal and South American sea lion.
For a birder, the Falklands are the most valuable of the three. There are land birds and grassland birds here that simply do not exist on the Antarctic continent.
The thing to check before you book is access, because "Falklands" on an itinerary can mean two very different trips. A ship that calls only at Stanley does not automatically include a king penguin visit. Volunteer Point, the famous king penguin site, needs an organised excursion, transport, enough port time and cooperative weather. A multi-island expedition programme is a different experience from a single port call, and the brochure will not always make that obvious.
Two smaller points. Macaronis do breed here, but in tiny numbers at specific spots, so do not come expecting a macaroni colony. And Magellanics nest in burrows, which is why guides keep you on marked paths: a collapsed burrow entrance is a destroyed nest.