Hands down I'd have to say; their undercover agent concealer; I use it all the time for under my eyes, not only does it cover the dark circles but it brightens the eyes and face.
tip if you wanna try it out; do not use too much of the eye brightener; I little goes a long way!
I love their "Nobody's Perfect" Concealer Palette, which brings many different color concealers to correct specific things.
I also love their blushes, baked blush and the fox in a box. They're my go to blush on a daily basis.