Chaozhou is at its best between October and April, when the weather is mild and dry. The summer months bring heat and humidity that can be oppressive in the dense old city lanes, and typhoon-season rains (June to September) occasionally make the riverfront impractical. October and November are the most comfortable.
The major temple festivals — particularly the lantern festival in the first lunar month and the Hungry Ghost Festival in the seventh — bring the old city to life with processions and ritual theatre. If you can time a visit around one of these, the experience of Chaozhou's religious culture at full intensity is worth the extra crowds.