The target tanks, both that you listed are good for lounging around at home and I lived in them without a bra for the first couple weeks PP with DD. But if you want to layer them under things or even wear them out... they are very thick and the straps are very wide. I don't think there really are specific ones, I think the only difference is a full sling or side sling (whether it unlatches and your boob sticks through a hole or it just hangs out with a bit of fabric on the side of it... I wear the side sling ones). There was one motherhood tank that I liked, it was light pink with lace at the top edge... but all the other ones, although they're not as thick as most, they are very very long and shapeless.
The only nursing bra that I have found that I love is from Motherhood Maternity, http://www.motherhood.com/Product.asp?Product_Id=911600361&MasterCategory_Id=MC29 the ladies there also said it's one of he most popular, and I like that it's comfortable, the straps aren't terribly wide and it's pretty... it feels like a normal bra which is rare unless you're going to spend $50+.