We had the same choice last year, my son is a 2010.
We chose the World because his travel team wanted him there instead. So I guess really we didn't choose.
Both are invite only events with I believe 80 teams so your chances are limited to be able to go. If you have the option to pick either your son must be a good player. I don't think it makes that much difference which event you attend but if he can go to the World he should attend IMO.
We are going again even though my son is committed to a college to enjoy the experience one last time. As far as who the scouts are looking at I would guess that 3/4 or more of the Seniors(10s) are done so the pro scouts are watching them and the colleges are on the Juniors(11s). Also, last year looking at the rosters I would say there were as many Juniors as Seniors at the event. PG STAFF may expand on this.