I put my MAC brushes in line to compare the sizes and shapes.
My faves are:
239 brush: perfect for pressed and loose eyeshadows
217 brush: I prefer this one to blend concealer underneath the eyes
224 brush: my absolute favorite crease blending brush!
214 and 212: great for smudging eyeliner and eyeshadow on the lower lashline
138 brush: great for subtle bronzers or highlights
109 and 116: prefer both for contouring and blushing