According to the search results, the best fruit for grinding in the 1st sea of Blox Fruits is Light, followed by Flame. Light has the fastest flight in the 1st sea, making it good for traveling and grinding, while Flame has a Z skill that deals extremely high damage. Venom is also a good fruit for grinding in the 1st sea due to its poison-tick damage, but it is expensive and difficult to obtain. Other fruits that are good for grinding in Blox Fruits include Magma, Rumble, and Buddha.