
Early game any of the rewards will increase your combat power, but I would personally focus on
Basic Treats
Basic Treats
Description
Feed it to Fantomons for 50 EXP.
Sources
Legion FarmingLegion FishingLegion Breeding
since those are harder to come by.

Gifts for companions take priority. A lot of companions to level up and never enough items to give them.

We start getting into the rewards that overall does not matter what you pick, all provide upgrades for your account.
I would take
Destiny Fruit
Destiny Fruit
Description
Search the world map for mysterious rewards. Remember, uncollected destiny resources will disappear after a while.
Sources
Delegate Tasks
since you have chances of getting bosses, merchants and great rewards with them.

DO NOT purchase
Stellatie
Stellatie
Description
Use it for Goddess Prayer to gain skills.
Sources
Delegate Tasks
or
Bond Trinket
Bond Trinket
Description
Use it at Arborisfatum to summon Fantomons.
Sources
Delegate Tasks
, those are available for F2P players.
The
Legendary Auroral Badge
Legendary Auroral Badge
Description
Use 10 to get a capsule from the Legendary Aeonic Gacha.
, on the other hand, are paid exclusive, so buy those.

Everything on this tier is good. Always check if you need the rewards available before you decide to spend.
I would 100% recommend getting the Lucky Statue to make daily grind easier.

