Please recommend Shard Farming SP Rawiyah or Safiyyah

Hello.

I have 3 stars SP Rawiyah and 3 stars Safiyyah.

I'd like to upgrade one of them to 4 or 5 stars through shard farming.

I'm aiming for 4 stars first, then 5 if I don’t have any other characters to work on by the time I'm done.

Can you please recommend whose shards I should farm between the two?