Is it better to be an average student at a more selective university or a top student at a less selective one?

Neither is universally better. At a more selective university, you may be stimulated by highly motivated peers and encounter a wider range of learning or extracurricular opportunities, although competition may be stronger. As a top student at a less selective university, you may have more chances to take leading roles and build confidence or achievements. Consider your goals, intended field, available support, cost, and where you can grow sustainably rather than choosing by selectivity or class rank alone.