Which is better, star idealism or materialism?

Idealism reduces differences, is suitable for a big empire, and can accommodate multiple species. Materialism develops science and technology, which can rapidly develop high-grade weapons and technology. You can choose according to your different ways of playing. For example, if you want to rule more aliens, then idealism will suit you better. If you don't want to make a sound, you have made a blockbuster and planted fields in your own galaxy for decades, then materialism will be more suitable for you.