# Hamming Distance vs. Index of Coincidence

When analyzing a repeating-key xor cipher to find the key length, I've read about two key methods (assuming there aren't just repeating chunks of ciphertext for Kasiski's method), for some assumed key length $l$, checking the Hamming distance of nearby chunks of ciphertext of length $l$, and checking the IoC for columns of text when the text is split into $l$ columns.

When are Hamming distances more effective, and when is the IoC more effective? Is there any way to know based on the ciphertext which technique will be more helpful, or is this a "try them both and now it's more an art than a science" sort of thing?