Studio Fix Fluid is a good product for everyday wear, but in my experience, isn't suitable for many professional applications. it contains titanium dioxide and can reflect bright in flash photography, making exact color matching in the finished image very difficult.
i keep a full range of cinema secrets palettes and about six shades of Make Up For Ever's HD line. I generally use the MUFE for those who need less coverage and CS for those who need heavier coverage, or longer wearing. I almost always use CS on brides.
I do have the full line of MAC's studio finish concealers, but I rarely use them. I've pretty much abandoned all MAC's foundations, even for my own personal use... and my skin is much better off since then.
PS- I do use quite a few MAC products, so it's not that I'm against them. I just find their foundations don't perform to professional standars.