The mages can deal very high damage with their skill and works great in manual play, but have issues in auto-play due to AI behavior. In manual, you can easily dodge enemy attacks to avoid getting hit, allowing you to play with full damage by increasing INT and LCK stats for most of the game's current content.
Flaming Dark Magic Crimson Wizard is a reward from the game's tower so it's not possible to reach +6 so quickly, which means he can't get 100% ST at the start of battle like Popoi or Angela. His attack recovers MP and ST deals damage in a very wide area, but INT buff skill comes with a self CON decrease.
Magic Power in Bloom Angela has the highest INT but short-range attack, which can often put her in dangerous situations. However, this comes with the benefit of being able to get MP when attacking.
Headed for the Home Village Popoi has decent AI behavior due to his weapon type being ranged, but his attack will not recover his MP. He has decent STR and INT since his ST is phys damage, while skill is magic damage, but this also means that he's a good character to use Mega Spirit Magic.
Highest HP, STR, and CON at max level out of the other 4★ Allies to be a good bruiser. Has a buff that gives Super Armor and increases his already high CON, and the other skill is an attack that gives a hard form of crowd control on small enemies with the addition of reducing their CON temporarily.
A tank that can deal decent physical damage from ST, but is also the only 4★ Ally that has a healing skill. This makes him a great support Ally to have to handle high-level content.
The most damage-oriented Ally out of the available 4★. She's a combo-based physical damage dealer with a STR buff and multi-hit attacks so she can build up her ST and combo counter somewhat quickly, as well as a dodge that can deal damage to maintain it.
A Wind element physical damage dealer that works similarly to Riesz. He has less damage, but higher survivability due to higher HP and +CON(buff). His ST attack is a 10-hit combo, which is great for building up the combo counter to increase overall damage right away.
Good bruiser-related and high ST damage. Becomes more unique at unleash +3 since he will be able to heal self and paired Ally after using ST.
These 3 are all free units that also come with free materials to reach +6, allowing them all to reach level 99 or 100 without having to summon in the gacha. This also means higher stats than many non-unleashed Allies to be used as the main Ally and higher passive skills to help the paired allies.
The only Ally that can do a party-wide heal and a cure to stun. A great support unit to bring but has low stats due to only a 2 star base unit. This can be considered an advantage since it's easier to get duplicates from summoning so she can reach +6 easier compared to 3 star Allies or higher.