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.