Despite the massive sprawl of modern Manila, many of the main attractions for tourists are located in the centre, and are quite close together. The city centre is well served by buses, and the Metrorail (MTR) system, that operated above the crowded streets and offers excellent value for money.
When you're on your way home from nightclubs in the wee small hours of the morning, its best to use a cab and agree a price before you set off to avoid any unpleasant surprises.
Hiring a car in Manila is pointless if you're not planning to leave the city, but is very cheap and liberating if you plan to travel further afield.