need a good +1 Weapon ability Pathfinder

[Nosta]

So I am playing a Half-Elf
Hidden Blade/Unchained Rogue

I am focusing on Mithral current and shattered
mirror martial fighting styles

I know I want to use a rapier
and I wand it mithral but I don't know what ability will
fit with my character build well

[Zsaber0]

Heartseeker to ignore concealment or Keen for a really big threat range.

[Drelua]

I was just about to suggest heartseeker, it's really useful and always gets an interesting reaction when you tell people that you have no miss chances against anything with a beating heart. Keen is, of course, a great option as usual. The only other +1s that really stand out are spell storing, if your group has a helpful caster, and bane, but only for a campaign that's really focused on a certain enemy type

[CharonsHelper]

I'm just going to say DON'T bother with keen. For most characters it's awesome on a rapier, but a large chunk of your damage will be coming from Sneak Attack which isn't multiplied on a crit.

As boring as it is, I'd stick with +bonus through +5. Rogues have some accuracy issues, so the accuracy bonus is pretty huge.