Three species on a standard Antarctic Peninsula trip: gentoo, chinstrap and Adélie. Gentoos are reasonably expected on a typical western Peninsula route and are the ones most often encountered. Which of the other two you meet depends on where the itinerary goes and which landings the weather allows.
Gentoo. White band across the top of the head, bright orange-red bill. Nests on open ground, beaches and low slopes. These are the pebble thieves. Their breeding runs less to a schedule than the other two, which is why you can see eggs at one landing and half-grown chicks at the next on the same voyage.
Chinstrap. The thin black line under the chin, like a helmet strap. Common around the South Shetlands and the northern Peninsula. Some colonies are enormous, but not every itinerary reaches a big one, so ask.
Adélie. Black head, white ring around the eye, compact build. Tied to sea ice and colder water. Reasonably expected on routes that visit the right colonies, less consistent on a short western Peninsula trip.
Three penguins you should not expect here: king, Magellanic and rockhopper. Those belong to South Georgia and the Falklands. Macaronis breed at a handful of Peninsula-area sites but are uncommon to rare, so do not plan around them.