Every certificate lists the same four grades. What it does not tell you is which of them you will actually notice once the ring is on your hand.
Cut comes first
Cut decides how much light comes back out of the stone. An Ideal cut returns light through the top in sharp, lively flashes; a weaker cut leaks it through the sides and looks glassy, whatever its colour or clarity. If you stretch anywhere, stretch here.
Then colour and clarity
Above G colour and VS2 clarity, the differences live on paper. In daylight, set in metal, a G and an E look the same to almost everyone. We usually recommend the lowest grade that looks colourless and eye-clean in the setting you have chosen.
Carat follows
Carat is weight, not size. Two 1.50 ct stones can face up differently depending on cut and shape. Once cut, colour and clarity are settled, let the carat be whatever your budget leaves.