Bobbi Brown vs. Mac liquid foundation (which is better?)?

The general consensus among beauty lover seems to be that MAC foundations suck. Bobbi Brown's are usually much higher quality, but you haven't mentioned WHICH foundations you are looking at. They all vary in terms of coverage and quality. The worst BB foundation is probably even worse than the best MAC foundation, so it would depend what your looking for. Read reviews online for a better idea of what different foundations are like. A good mattifying primer is Tarte's Clean Slate. Makes my oily face smooth and matte, plus it's paraben and petro-chemical free!