The best time is subject to the city, weather and the kind of experience you want! People usually favour the mornings, when attractions are less crowded and they can see more during the day if they travel many times. Open top buses can also offer great views in fine weather. Hop on hop off bus services are generally busier on weekends, holidays and during busy tourist seasons, so it may be wise to reserve tickets in advance. Weekdays may be more suitable if you prefer a more quiet experience. Also be sure to see hours of operation, as some would run differently during certain seasons. You can plan your sightseeing so that you can do more with your ticket and have a more comfortable travel experience.