On the first trip I used a company called Anywhere Costa Rica to arrange for private or shared shuttles to drive us around, and that was great. I actually learn cool information when talking to the shuttle driver, like how the healthcare system there works and stuff like that. I don't think I have the nerve to drive in Costa Rica myself because I'm such a "what if" person (what if I get a flat? what if the road is washed out? etc.). I will say that the road signs in CR are NOT well marked, so a GPS device is essential imo. I remember thinking on that first trip, how could anyone give me directions that would make sense to me? Like "turn left at the pink house" since there's no street sign to help me out (what if it recently was painted white?). The main highway roads are well paved, but the ones you take to get to the final destination can be narrow and rutted dirt roads. I know lots of people have rented cars successfully, but it's not exactly cheap to rent either. A lot of the day trip companies will actually pick you up at your hotel, so if you're doing those then transportation is usually included.
The Andaz looks beautiful! We'll have to try that one!