For reference, I am an NC20, with yellow or beige undertones.
I had been using MAC SFF and Revlon Colorstay for more than 5 years now.
Buff Beige is lighter on my skin.
I love the sand beige on winter, but I think I can get away with a medium beige during summertime.
Or you can mix both to create a wonderful combo.
Here is a color chart of Revlon Colorstay as compared to MAC SFF.
Hope it helps.
Color chart for Revlon Colorstay vs MAC Studio Fix Fluid:
Ivory: NW15/ NC15 lightest of the bunch
Buff: NC20 best match for fair NCs
Sand Beige: NC20-25 with somewhat neutral undertones
Nude: NC25 with peachy undertones, definitely not for pinks or true golden
Natural Beige: NW20 tends to run pink
Medium Beige: NC27 between Sand Beige and Golden Beige
Fresh Beige: NW25 with pinky undertones
Golden Beige: NC30 with truest yellow/olive undertones
Warm Golden: NW30/NC30 with somewhat neutral undertones
True Beige: NW30 with pinky undertones (for Fresh Beige in summer)
Natural Tan: NC40/NC42 more neutral than golden caramel
Early Tan: NW35 with somewhat peach undertones
Rich Tan: NW35 with pinkish undertones
Golden Caramel: NC40/NC42 more golden than natural tan
Toast: NW43/NC45 with neutral undertones
Rich Ginger: NW45 very peachy-pink
Caramel: NC45 seems to run true to color
Cappucino: NC50 slightly more peach than Caramel
Mahogany: NW50/NC55 the darkest of NWs but not extremely peachy
Mocha: NW55 seems to be very cool toned, almost grey undertone