We have an Assassination Rogue and a Dual-Wielding Champion Fighter in our party, and we often divide our items trying to maximize party damage output. One pattern that we have noticed is that any weapon that works for both characters is better suited for the Fighter. With his Extra Attack, the Fighter will always cause the weapon to do more damage than the Rogue (who has a single attack).
Currently, the Rogue has two +1 daggers, and the Fighter has a +1 shortsword and a regular shortsword. The Rogue was given both daggers just to ensure Sneak Attack could land as magical damage. They've not picked feats yet and will reach level 11 next week. Both have maxed out their Dexterity scores.
However, as more weapons are found now (Vorpal Swords, Sun blades, etc), it seems like the optimal strategy is to always give them to the Fighter first, and his 'leftovers' are then given to the Rogue. Since they will now both have 2 magical weapons, the Fighter is always the best choice, DPR-wise.
What kind of magical weapon (if any) is better suited for the Rogue rather than the Fighter?
Best Answer
Avoid Pure Damage
A magic weapon can do a lot of things other than buff your damage. A Weapon of Warning, for example, gives advantage on initiative rolls, and thus would be perfect for an assassin rogue. A Dagger of Blindsight (from Waterdeep: Dungeon of the Mad Mage) would be equally appropriate, allowing an Assassin to skulk around even in magical darkness.
Fighters get Extra Attack, and so they can leverage extra damage well. You need to find a way to leverage what you have (benefitting from going first, benefitting from advantage, et cetera).