I wear a lot of these style tank tops because I run hot, fast metabolism. Which is why on one hand these are great because the material is thin, soft, and doesn't cause me to overheat like some thicker tanks. Only thing is they are transparent. The white ones almost completely, the black are better, but the way the style is there is a  different vertical texture  starting right about nipple area(for me anyway) to arm pit area, and that different texture is slightly ribbed and thinner, which makes it the transparent zone on the black tanks.

I got a medium, I usually get medium tanks and medium or large t shirts. They are comfortable, but better for an undershirt if your going in public. Around home who cares!

EDIT: After wearing these for a few weeks I decided to try a different brand. Besides being thin, they are short. If you OVER 6 FEET TALL GET A LARGE at least. The mediums will just barely sit at the top of my pants/shorts, until I move then I'm showing boxers or skin. I might order another large set in white for really light undershirts or hot days, but I think I am getting rid of the black and white mediums I got, I kind of hate wearing them compared to my new ones. (which are DKNY by the way, Little more spendy, but in my opinion they are on par with Stafford, my old favs.)