I feel like an anomaly here because I really like MAC foundations!
Seriously, I've always had trouble with foundations breaking me out---not just pimples, but hives and welts. Definitely allergic to something in a lot of cosmetics but not sure what it is. Anyway, I have never experimented much with different lines. If one product in a line makes me itch, I generally move on and don't try the line again. And if I find something that works, I stick with the line.
For years I wore Clinique foundations but was never totally satisfied because, no matter what formula I used, eventually the foundations changed color on my skin. I was also clueless about undertones so I probably wore the wrong color as well. On a whim, I decided to try MAC and bought a foundation (Select Tint, I think) and an eyeshadow. Neither one made me break out so I felt safe trying other MAC products.
MAC foundations don't change color on me, which I like. I have combination skin, oily in the T-zone and hairline and dry cheeks. I live in an area that's cold and dry so I need makeup with a little bit of moisture. I stopped using Select Tint because it was a little too sheer and I prefer cream-to-powder. Sometimes, in the summer especially, I wear Studio Fix powder but lately I've been into Studio Tech. Studio Tech gives me good coverage---I find I use much less concealer with this formula. I also like the way it feels on my skin. It doesn't get patchy in the dry areas and, if the T-zone gets oily, I use a blot paper to decrease the grease.
The other thing I like about MAC foundation is that the colors work for me. I wear NW20 in Studio Tint, N4 in Studio Fix powder and NW20, cut with a little NW15, in Studio Tech. I have pink undertones but there's quite a bit of yellow in my skin, so MAC works well for me. However, others say that MAC is too yellow, even in the NW shades.
You know, I don't think there's any middle ground here on MAC foundations. People either love them or despise them. Try them and see where you fall. Good luck!