I try to make sure that I always have a small (500ml)bottle of 8% in stock and full size (1L) 10% and 12%. There are a number of clients out there that just cant get a suntan, Freckles, really fair skinned etc and they LOVE the 8% but other than them the 12 is very popular for me in the Spring and Summer with the 8 and the 10 doing better in the winter. It does depend on the area you are in, where I am people like the natural glow rather than the "David Dickenson" look.LOL
I love the look on those fairskinned girls faces when they see a fabulous natural color on their skin after years of being lily white, makes you feel all warm and fuzzy inside.LOLSM
Good luck with the shopping,
PS I sometimes mix colors as well to make up a color , bought a 16 once, never used it so mixed with 10 for a 13 and with an 8 for a 12 and so on. Some clients loved the fact that I was "Tailoring a color" to suit their skin tone and color. ( They still come back... good customer service)