This really depends on your preferences....I've used both with my kids, and I really like the backpack for places like airports and places where the terain doesn't allow for a stroller. Backpacks are also great when it's difficult to get through a crowd with a stroller which is probably why you're considering that. Although they're more maneuverable, you do have to be a little more careful with a backpack....it's easier to not realize that you're bumping into something, and the kids can reach more from that position without you knowing it.
I personally prefer a stroller though when feasible....
I think the biggest advantage is that you can see your child's face, reactions, etc. which is the whole reason you're probably going. Also, strollers are easier to get the child into and out of, aren't physically taxing, allow the child more room to move/play/snack, and don't heat up both you and your child (which is mostly a factor if you're visiting when it's hot.)
If you're going to be there for a while and will be going to/from parks, you might want to bring both with you on the trip and just alternate which you use depending on where you're going, time of day, how long you'll be there, etc.
Have a great trip!