It depends what you are looking for.
Both of them have few free areas to roam around and if you want to get more just either purchase membership or/and buy areas (the areas you purchase -not buy membership- will stay open for you for ever )

Wizard101 has more activities you can do as a free player (Beastmoon, Deckathalon, etc). Pirate101 has zero side activities. You get more options as a F2P in Wizard101.