It really is a personal choice, what you have and what the client likes.. most importantly.... he he.... Most people these days go for either forever french or variation...
I personally (using Creative) find the majority are now going for perfect white with perfect powder intense pink, these used with Moxie gives an amazing 'pop' to the nail!!
Alternatively there is the custom blending kit, so for those who are prepared to pay a little extra they have a custom colour for their skin tone.... Ie warm skin, warm colours, for both free edge and bed colour! - love it!! just like facial foundation, everyone is a little different.
And ocasionally, you get those who want metallics (metro's) colours (mosaic) and art, very cool.