Yes, I mix.... That way, I get what I need and want and am not restricted to what JUST ONE particular line offers.
Whole one line may have nice lippes and or e/s, their foundation and powders might not suit my skin tone and type....
Some of my friends are makeup snobs. They only use one or two lines, exclusively. Others don't bother with d/s or mid-range price brands and choose high-end or designer makeup only.
I use what works for me. I don't care if a product has fancy packaging or a "famous" name attatched to it. (EX: Jessica Simpson.... or Dior.) I do, however, look at the pricetag. Some products cost just waaaaaaaaaay too much......
My criteria for product selection: (not in any particular order)
* What does it do for my skin? Does it work with my very oily and sensitive skin?
* Does the texture and color work for my complexion or the purpose I want to use it for? (Great if it's a multi-use item, like some bronzers or blushes. You can use it as an e/s, blush, lip product (mixed with gloss or balm,) contour product or bronzer.
* Will I use it regularly, or is it a "special occassion" item, only. For more of a "special occassion" items: if it's inexpensive, I may buy it; if it's pricey, I'll have to think about it.....
In some cases, I have found products from other lines that work the same way, look the same and cost 2-3x less than "fancy" lines. Only in a few cases where a higher-end product has outdone a lower to mid-range product, have I chosen to buy the higher-end product. (Ex: Shiseido's lash curler at $16 versus a d/s brand curler at $5-10.)
I'd recommend mixing brands. Think about what you want and what works for your skin type and complexion. And lastly, don't forget to think about your wallet.