There are two configurations of reinforcements that are considered optimal.

Sharpness EX, 2x Attack EX, 2x Attack III

This is tricky to roll but gives you the highest true raw on your weapon. It leaves you with 15% base affinity on your weapon so you will need to gain the rest through your armor skills.

Sharpness EX, 2x Attack EX, Attack III, Affinity EX

This is several times easier to roll than the other configuration, and performs virtually identically. It leaves you with 25% base affinity on your weapon so you must take care not to overcap your affinity with armor skills.

Suboptimal Configurations

The most important thing is to have one Sharpness reinforcement minimum, or the weapon won’t be practical to use. After that, try to get as many Affinity/Attack and as few Element reinforcements as possible.