the cutting of the round diamond shows most of the brilliance. It is expensive because it waste a lot. the princess is cheaper, since the cutting won't creat so much waste, and it is not as brilliance. the cushion cut gives you a small tale in the same weight, so makes the diamond looks smaller. emerald looks more tranditionally but least brilliance. and the pearshape does not have a lot of availability in the market.

Hopely it helps.