Greatballs are premium Pokeballs that boast a higher success rate in catching Pokemon compared to regular balls. You can receive 20 of them starting at level 12, and they become available at PokeStops or upon reaching level 12.
Ultraballs are arguably the most premium Pokeballs currently available (excluding Masterballs). They have a significantly higher success rate than Greatballs and are only obtainable at level 20, with 20 available at PokeStops from level 20 onwards, although their success rate is lower than Greatballs.
The last type, Masterballs, is one that Mytour hesitates to include in this list due to its rarity and the scarcity of information surrounding it. With an incredibly low chance of appearance, Masterballs boast a 100% catch rate for common Pokemon. However, their effectiveness with legendary Pokemon remains unconfirmed.
With the four types of Pokeballs in Pokemon Go as of the current time, it's evident that the game's appeal extends beyond simply throwing balls and catching Pokemon. If unable to catch higher-tier creatures, capturing numerous lower-tier ones can still be beneficial for upgrading or evolving Pokemon. Whether you use them for candy fusion or to strengthen your Pokemon is up to you, but it undoubtedly saves time compared to pursuing high-tier catches.