I use the black-bottomed take-out containers from Amazon (link). I like them over regular tupperware containers because you get so many of the same size (I'm often prepping 8-10 meals at once), so they stack well in the freezer. I could buy more durable ones, but that would cost more money. A lot of the time I feel like I use something like this for a while, then decide that I'd like a different size. Or I stop freezing meals for a while.

This way I can use these for a few months, stack them neatly in the freezer and then recycle them when my needs change, and I'm only out $10.

I was thinking of reordering these from Amazon because my mom lost 3/7 of mine, but then I found similar ones for a better value at Sam's.

I think the brand was Snap Pak. 50 count for less than $20. Same quality and size. Slightly rounded out on the long sides. Highly recommend.