Dual Enrollment or other summer online course?

<p>Hi everybody! I am new here. My questions: My son is a junior this year (ending soon). He is interested in taking some online courses during the summer. Which one should he choose between dual enrollment at a local college (online) and other online courses such as AoPS, CTY, or EPGY? Does it really do any good or bad to him regarding college application? Would that affect his GPA in HS? I need to consider this because first of all it IS expensive. Thanks a lot for any advice!</p>