Which is better for achieving strong long-term growth: owning a handful of strong stocks or holding a larger number of stocks?

Which option do you think is smarter for achieving strong long-term growth?

Is it better to take more risk by investing in only a handful of high-quality stocks, or to reduce risk by investing in an entire sector, a broad market index, or even just several dozen stocks for greater diversification—even though spreading out the investment may make it harder to achieve exceptionally high returns?

Which approach do you think is better? and why?