This can depend on your individual choice or needs plus obviously your budget. The spec or space in a car that you prefer might take preference over the make and model that you decide to go for.Like anything else, test drive different cars and see what you like.
Nissan Micra or Toyota Yaris tend to be most buyers preferred or number 1 choice. Tend to be plenty of these cars available but you will pay more for than you would for an OpelbCorsa or Citroen C3 etc.
Depending on your budget I'd advise you if you know a mechanic or have a look on donedeal.ie or adverts.ie for second hand cars.