I have a question:
What is the best way to stamped my response envelope to America?
I'm from Germany and I would like to contact Will Smith via Venue.
My lasts letters i have put in two IRC's, but I have heard that USA stamps are better. Or shoud I have to print online a shipping label at: https://sss-web.usps.com/cns/landing.do
Is that good and also for germans?
My Letter:

Size: DIN C4
Thanks in advance for your kindness
Denis