When do we say "My Lord, provide for me" and when do we say "My Lord, grant me"? And which of them is better, and what is the difference between them?

Allah, the Exalted, is Al-Razzaq (the Provider) and Al-Wahhab (the Bestower). He provides and bestows whatever bounties He wills upon whomever of His servants He wills. Provision (rizq) and bestowal (hiba) both share the characteristic of being a gift from Allah, for all blessings are a gift that Allah provides and bestows. "Rizq" encompasses every gift of worldly and religious blessings, while "hiba" is a gift given without recompense. There is no fundamental difference between saying "O Allah, provide me with such-and-such" and "O Allah, bestow upon me such-and-such," as both signify asking for Allah's gift and generosity. There is no need for overly meticulous linguistic scrutiny in supplication; rather, the servant should supplicate using whatever words come easily to them with a humble heart, for Allah knows the intention of the supplicant even if their tongue is not perfectly eloquent.