What currency to bring ?

I've tried to find answer in the sub but it's still not clear yet:

I will be visiting this country that look amazing in late February but I still don't know what currency I should bring with me, to be clear, I live in Europe:

- should I bring Euro in cash and change it in Riel at the Airport ?

- should I "buy" Riels at the airport with my Visa ?

- should I change euros to USD in Europe and change it at the Airport or at a bank in a city ?