It depends on the situation. You would say "this one or that one" if, in your mind, one alternative was farther away or more remote. Imagine a salesperson showing you a green shirt and a blue shirt.. He might hold up the green shirt and say "which do you like better, this one..." Then he might put it down and hold up a blue shirt and say "...or this one?" "This" means "the shirt I'm showing to you right now." I might say "I prefer the green shirt." And then he might say "Shall we wrap that one up for you, then?" He's still holding up the blue shirt, so the green shirt on the table has become "that shirt."

Hi Vivaldo, Both are correct. "This" could imply close to you and "That" further away, but that is not a hard rule, as I understand. Let's say you have two books on the table and you tell me to read one. I could point to the first one and say "This?" and then the second "Or that one?" So you can say either way. Nicolas

"This one or this one?" is easer to understand :)