Old Navy completely lost its shape after three washings for me. I gave those away.
I the J. Crew favorite tank for colored wifebeaters and I buy Fruit of the Loom boys wifebeaters in an XL. The FOTL boys' beaters hit at around mid-hip on me. I would like to get longer ones too, so I may try the mens' S. I remember trying the Hanes mens' wifebeaters in an S and they were literally down on me all the way to midthigh.
I like Jockey wifebeaters for women. I think I got mine at Ross for $2. The stretch and fit is perfect on me. I also like J.Crew favorite tanks because they come in lots of colors and they're long enough on my torso.
j crew favorite tank by far my fav for wearing under stuff- they shrink in the dryer but go back to normal size when wearing in my experience- have lasted 3 years so far- and still look good!
recent fav- bought at TJmaxx, have also seen at marshalls- by calvin klein- they have them in black, white, grey and seafoam green- nice and long (if i pull it down as far as it can go, it hits mid butt, but i am petite) even after washing, nice amt.of stretch for fit (93% cotton, 7%lycra) and they are racerback, which i love. i haven't had them too long so i'm not sure about longevity yet