Depends on your definition of best.
And if you are set on dropping (maybe moving for example) or just looking for better pricing.
If set on dropping regardless of any possible deals, I would say store.
Especially if you have TV with their STB. Take them with you to store so you can turn them in.
If looking for a better price or maybe just have Internet, then try phone.
They may send you over to a retention department who can try to offer you a better deal.