air travel – I would like to book single round trip ticket from USA to China, but would like to have my friend in the same plane in my return trip back to USA

Me: USA to China (round trip)
my partner China to USA only.

But I would like to have my partner in same flight and next seat.

or should I book like, single one way ticket from USA to China and 2 one way ticket from China to USA for both of us.

which is less expensive? any thought or suggestions?

Thanks