Choosing the base currency

Hi,
I am just now signing to one broker. He asked me what my base currency would be, and there is several options. So at first, I thought that it is not such an important factor, but now that I think about it, I think it maybe is. So how should I choose the best base currency?

Also He told me to leave the dates blank? Can that be misused?

What is your currency?

USD is the World reserve currency.

It is important.

Sorry that I wrote this - I've just noticed that you answered to that.
I would still like to get an answer to the second answer - Can the leaving of the blank date on contract papers be misused?

Do you mean the contract you are signing with the broker?

Why would that need to be blank?

Since I live in Serbia, it is RSD, but we use EUR a lot.

My broker to be wrote me that i should leave the date field blank

I doubt they would fund your account in RSD.

You should use Either USD, EUR, or GBP in my opinion.

Is this application online? or in paper.

Also when the account is funded the date should be recorded.

Honestly I don't like the idea of not writing a date. What is the reason?
What if you have a dispute on X date and they tell you your account was not
live at that point. Then what?

Do you mind my asking what the broker is?

I should print the papers, sign them, scan them and then send him back