thin black plastic. they look good on almost everyone

It depends on the shape of your face -- and whether you want to go with the trendy frames that are so popular now. Also, if your lenses are thick due to bad eyesight then some frames are better than others in that case. I personally like the trendy smaller frames. Ultimately it's what you think you look good in. Maybe this will help: STEP 1: Pull your hair back in a ponytail (if necessary) and inspect your face shape in front of the mirror. STEP 2: Keep in mind that oval faces are egg-shaped and balanced on top and bottom, and can support any type of frame. STEP 3: Make a long, thin face seem wider and shorter with larger frames in round or triangular shapes. Or try a wide, rectangular shape. Frames that have color, width or embellishment near the sides will also broaden your face. STEP 4: Try round frames made of thin metal to soften the angular look of a square face, which has a wide forehead and cheeks, and an angular chin. STEP 5: Remember that round faces are fuller, with a gentle chin, wide cheeks and small cheekbones. Avoid round frames, which make the face look larger; wear boxy or rectangular ones instead. Dark frames can weigh down your face, making it appear heavier. STEP 6: Balance a heart-shaped face, which has a wide forehead that angles down to a small chin, with frames that are wider at the bottom than at the top. STEP 7: Flatter a diamond-shaped face, which has a narrow forehead, wide temples and an angular chin, by wearing small frames in geometric or oval shapes to minimize the horizontal distance between your temples. STEP 8: Choose smaller frames if you have facial hair such as a beard. Large frames will further mask your features. STEP 9: Stick with small frames if you have a small head. Make sure your glasses aren't any wider than the widest part of your face. STEP 10: Select large frames that fit comfortably if you have a large head. Avoid glasses that appear to squeeze your face or temples.