Dual enrollment at a college campus will expose them to greater diversity in terms of traditional and non traditional college students as well as high school students. It will also be a taste of actual college, rather than just college level material that may be found in AP courses. If the student wants to go to professional school (e.g. medical or law), college courses taken while in high school and their grades will count when calculating college GPA for those applications.
IB is generally considered to be a lot of work, and the curriculum for the full diploma is relatively rigid. Check which subjects are offered in which variants (SL or HL), since some IB programs offer only one variant of some courses.
In terms of transfer credit, take a look at what colleges of interest accept from each option.