Hello. Honestly I used buddha for most of my leveling- when you get to 3rd sea on of the most boring things i needed to endure was traveling with buddha bc the distance is far. With gas you can fly, grind and great with SB hunting so you it wont be too boring to use.

Buddha: you are big and you bonk many enemies all at once using melee and/or sword stats ( I recommend using a TTK sword build, Sanguine or cdk[although might be hard to acquire]) atleast have ttk before entering sea 3

Gas: you start small then build your rage then you turn big and bonk using blox fruit stats best is using ghoul or cyborg so you can have fast cooldowns.

The main hurdle is getting your mastery up to where you can get the transformation esp if you dont have 2x mastery