Two shade that will go head to head for my attention because they are SO similar are Mac Cosmetics Vintage Vamp and Sally Hanson's Hard As Nails in Flirt.
As you can see they are really really similar so one could almost say the Sally Hansen (approx $4-$5) could act as a great dupe for the Mac polish ( , and while I would agree they are not 100% alike. Just look at the stock photos, the SH polish is NOT that purple in real life.
I found Mac's Vintage Vamp more on the red brown side with no hint of shimmer while Sally Hansen's Flirt is more on the red purple side with the slightest fleck of shimmer that shows only in bright light.
See for yourself... Can you tell the difference?
Similar yes but I'll be rocking BOTH of these amazing vampy shades equally this fall ;)