I mean, I'm partial to Pyrex, and I've been meal prepping for over five years now. The 3-cup containers (rectangular or round, like from a Pyrex variety pack, because I'm not going to not use a perfectly good container just because it doesn't match the others) are the perfect size for a meal for me. I also use mason jars for freezing portions of soup, and I have a few pint-sized Talenti gelato containers for stuff like overnight oats, or cottage cheese and cherry tomatoes.

When I started, I used white plastic takeout containers from the local sushi place, and finally switched to Pyrex because the plastic containers were cracking and warping, and I was tired of not being able to prep tomato-based foods unless I wanted a bunch of orange-stained containers.

I used cheap plastic takeout containers saved from the local sushi place for years- basically these, but in white. They went in and out of the freezer, microwave, and dishwasher that whole time, and none of them leaked and the lids still sealed. When I moved out of my parents' house and got my own place, I switched to Pyrex glass. All of my lunch containers have a 3-cup capacity, and I have the rectangular ones, and the circular ones. I also have eight pint-sized mason jars that I use for overnight oats or soup. The dishwasher is hard on plastic, so I always hand-wash the lids, and I don't microwave the lids, either.

With Pyrex/glass, they're heavier (and so not great if weight is a concern, or if you bike to work or something), more expensive, and you do have to be careful not to drop them or temperature-shock them. So, like, don't put piping hot food in them and put them straight in the freezer, for instance. But glass lasts a lot longer, you don't have to worry about the health concerns of microwaving plastic, you can sterilize glass in the dishwasher without it putting out microplastics, it cleans up better than plastic, and it doesn't stain if you make something tomato-based.