The old town and souq are walkable. For anything further afield — Shubra Palace, the parks, the Al Hada road, the rose farms — you need a car. Uber and Careem both operate in Ta'if and are reliable and inexpensive. For day trips to the rose farms or Al Shafa plateau, hiring a driver for the day is the easiest option.
Most major car rental firms have offices at the airport. Traffic in the centre is moderate; the steep approach roads should be driven carefully, especially the Al Hada switchbacks.