It depends on your strategy. However, by default, If the opponent has a higher win % chance against your character due to the below it’s advisable to reroll for a better opponent to defeat.
- Enemy character has a elemental advantage against your character
- Enemy character has a higher power due to higher level in Tiered PVP
- Enemy character has a higher stats/tier of weapon and shield
- Enemy character has elemental alignment on weapon, shield and gear sub-stats