I've dabbled with quite a few concealers. Most of them I use all-around (for both undereyes and blemishes) but I'm seeing the value of using separate products. Here are some quick thoughts:
NYX concealer in a jar - good color match and coverage (there's a peachy undertone that makes it good for undereyes), weird scent, a bit heavy and oily texture, fades even when set with powder, creases badly when used on the undereyes
Revlon age defying moisturizing concealer - nice texture, ashy for my NC35 skin but kinda melts into it eventually, light-medium coverage but fades by afternoon, can be used to brighten spots on the face but not conceal them
Revlon photoready concealer - good color match, good coverage, creases slightly when placed on the undereyes, drying so you need moisturizer underneath, fades a little by afternoon, has sparkles but not obvious
Laura Mercier secret concealer - nice texture (not too thick, not too thin), good color for dark undereyes, creases a little, buildable coverage, fades a little by afternoon
Am now testing the Zero Kuma concealer for the undereyes and the Artdeco one for blemishes. Seems like a good combination so far.