After around 100 level 100 dungeons, it definitely feels like the choice option between dungeon battles could be revamped some. Currently, there is nothing exciting within the two choices that make for much of a game changer. There are also none that have a risk/reward kind of system that makes the dungeon even harder, but rewards more for doing so.
I have two main suggestions:
1: Make the 2 choices into 3 with the choice always between offensive, defensive, and loot.
2: Make different rarity bonuses so it is actually exciting to get a rarer good choice.
Exact specifics could be pretty much anything, but some of them based on rarity (also including existing ones) could be things along the lines of the following.
Gain Weapon Damage
Gain Max Ultimate Meter (150 mana), but drain all other mana
Go straight to the final boss, but lose all mana and positive status effects
Reduce HP, armor, and resistance to 1, but triple power and weapon damage
Gain Armor and Resistance
Lower Power of All Upcoming Enemies and Yourself
Gain Barrier, but lose weapon damage
On next death, revive, but with no mana and 25% durability (same way a coop dungeon death works)
(All uncommon and rare require a dungeon clear to receive, otherwise nothing.)
One Random Drop from the dungeon, but half power and vitality
Duplicate Chest at end of dungeon, but shuffle the board and give next enemy full mana
Guaranteed Ruby Chest, but dispel all positive status effects and drain all mana
Guaranteed Diamond Chest, but dispel all positive status effects and drain all mana