Beach...2012?

I have a dilemma, but it requires a little explanation, so bear with me. I get two weeks vacation next year, but have to sign up for the specific weeks well in advance. Vacation sign-ups are done by shift and seniority, and involve other restrictions as well(no more than two people on a given shift can sign up for the same week, you can't take a week if someone else higher up in your line of progression has already taken it, that sort of thing). Attempting to keep this as concise as possible, in order for me to go to the beach next year (assuming we want to stick with our middle-of-September timeframe) I am going to have to swap a week with one of two guys. Each have expressed willingness to do so, but I need to figure out in relatively short order which of those weeks I want so I'll know with whom to swap, and that person can begin rearranging his schedule. Do we want to shoot for the week of Sept 9-15, or 16-22 of 2012? I know this is a ways out and all, but does anyone have a preference or restriction for one week over the other?