I think both of your choices (Buenos Aires or China) would be cool. I've been to China but not BA.
Other than the cost of the plane ticket, everything in China is very inexpensive -- food, logding, etc. etc. You can buy silk ties for $2, which would cost $40 each in the US. I bought 3. I should have bought more.
I ate dinner with 4 other women and the entire meal for the 5 of us cost $8 (including a large entree for each of us, soup for all of us, eggrolls, two appetizers that we shared, and 5 soft drinks).
Have fun dude whatever you choose. Travelling has been an important part of my life over the years. I don't think you can go wrong as long as you keep doing it. Besides, you will always have cooler stories to tell than your friends.