i think it really depends what msf you're using and what you're using if for.
i use the msf natural as a contour color and apply it with the 186 in the hollows of my cheeks and with the 109 around my temples and jawline.
for the more colorful LE msf, i either use the 187 if i want a subtle glow of color on my cheeks or the 116 if i want a bit more intense color.
i personally don't really like the 134. it's pretty big, and thus good if you want an all-over dusting of product. for me, i needed a more controlled application for the flashtronic msfs or i just end up with a face full of shimmer.
hope that helps!