In the spirit of this question, which Mitzva has the most halachot? If it is hard to pick one, happy to hear about a "top 5" etc.
E.g.
It is hard to measure which Mitzva has the most halachot, as that's too loose a definition of how a Mitzva breaks down. However, it certainly seems that these Mitzvot X, Y and Z play a huge role in the Shulchan Aruch compared to other Mitzvot
would be a fine answer. Or even "there is no answer to this question, as there are many halachot for many Mitzvot and there are no clear outliers for the most"