Joining a half-day or full-day guided tour of Cappadociais an excellent idea because the region's local publictransport network is weak.
Renting a car is a good but not perfect solution to the public-transport problem because finding your way around Cappadocia is tricky in some areas because of poor signage. A GPS is helpful, but not always accurate.
So for many visitors, a guided tour makes sense, at least for some of your touring. Here are the tours I think are recommendable:
Rock Valley Travel
Rock Valley Travel, a long-time proven quality travel agency (and a TurkeyTravelPlanner.com partner) has an excellent list of Cappadocia tours covering all the major sights:
Blue Cappadocia Tour
The Blue Tour is the perfect full-day tour for your first day in Cappadocia, hitting all the top sights in the region of Göreme, Avanos & Uçhisar: Göreme & Zelve Open-Air Museums, Uçhisar rock castle, Devrent & Paşabağı valleys, Avanos and Esentepe. Lunch is included. More...
Red Cappadocia Tour
The Red Tour, for your second day, takes you to places where you can walk and explore even more: Derinkuyu Underground City; Ihlara Valley & its rock-hewn churches and villages of Belisırma and Selime; Agzıkarahan Seljuk Turkish caravansaray. Lunch is included. More...
Green Cappadocia Tour
If you have a third full day in Cappadocia, the Green Tourtakes you to the next tier of sights, less well known but no less interesting: Kaymaklı Underground City, the less-visited Soğanlı Valley, the Roman city of Sobessos with its mosaic-floored houses, the ancient medrese (theological college) at Taşkınpaşa; Keslik Orthodox monastery, and the Ottoman Greek village of Mustafapaşa. More...