I bought a variety off of Amazon, I found that I like the Bravado brand the best as far as fit and comfort. I also bought a Amoralia second skin nursing sleep tank, it was pricey but feels like heaven.
I got 3 from walmart. They are extremely comfortable and seem like they are going hold up. They have a 2 pack for 16 dollars and I got one on clearance for 5. Mother hood also has good but they cost alot more.
Motherhood has great ones, I loved the ones I got there. But just as useful for me were the nursing tanks I got at Target and those were wayyy cheaper. After the initial engorgement phase I was able to wear regular sports bras and just tuck them under my boob while nursing... but having the nursing bras was awesome, I liked the convenience and discretion factors.