Good question, I only have Arjuna alter and he hits hard thanks to his NP effect.

It depends who you Like more, though in many case, Arjuna Alter seems can do better than Amakusa. But if you're still not sure who to roll, then don't roll at all. Wait until you see a servant you really want to roll without thinking.

The same question, only Dantès is added to these two

The same answer, only Dantes is added to these two.

Sometimes the best thing to do is do nothing, or in this, roll nothing. If you don't know who to roll, then don't roll at all. Simple as that.

Arthur appeared there, whom I chose without hesitation. I just wanted to inquire about the supplement to it.

Then imo, choose Arthur, forget anyone else. They all will have return banner one day, maybe, but atleast you'll get your most wanted servant.