okay...MAC brushes: my personal essentials are the 187 (i have two, one for cream, one for powder products), because this brush is just the best thing ever. MSFs, studio fix fluid, anything. controlled, even application, pricey, but worth it. IMO the flirt skunk brush does NOT compare, as you just can't put a $6 brush and a $42 brush side by side and expect them to do the same things. the 168 is a good blush/face contour brush, and is really the only blush brush i use with any regularity. if you want to spend the money, go for the 150 powder brush as well. i have the 190 foundation brush, but PREFER the smashbox foundation brush. it just is easier to work with, and i find it distributes the foundation better, and more evenly.
eyes: 266 for liner and brows is a must. 239 is the best brush ever for packing on colort, 272 and 228 for detailed and blending work, 228 is particularly good at working with pigments since its SO tiny and cuts down majorly on fallout. plus, it really packs on color in tiny places. 252 if you want something thats pretty good at color washes, and 217 to blend. i don't really use lip brushes.
too faced had a brush set awhile ago that was 5 or 6 brushes (blush, several eye, etc.) that came in a hot pink and leopard print case that was like $45...iif you can find it, get it, as the brushes were all amazingly good quality. i got it at sephora like 3 years ago, and the brushes are still in excellent shape. sonia kashuk and nars have pretty good brushes as well. IMO, the full size brushes are worth the extra money, as i've found that the brush set brushes generally aren't as good quality. plus, i like the longer handles better. go to a counter, try some brushes out, get a feel for what you like, because everyones brush preference is different.