Gioan, I don't think anyone is going to be able to tell you what to do, because it's going to depend not only on the specifics of the schools but on your own family values.
Questions I would think about and/or ask:
1. Will your child actually complete the IB diploma? If s/he doesn't, do you think the school is worth attending anyway?
2. What kind of counseling services is your family likely to need, and are they available at both schools? For example, do you feel comfortable with the expertise at each school in helping you figure out which colleges are a good fit?
3. Is it important to you that your child be exposed to other children from diverse backgrounds (socioeconomic, racial, whatever)? If so, which school will serve that best?
4. Is the GT program a "real" program that strives to improve deep understanding, or is it primarily extra busywork? How about the IB program?
5. What do the post-high-school paths of the kids from each school look like?
6. What does your child want to do?
