Rubbermaid, Sterilite, or Iris?

[jglass38]

I haven't actually used any myself, but the Iris tubs I've looked at in the store seemed really thin and flimsy, like they would crack very easily.

Not in my experience. Sterilite cracks the easiest, then it's probably a tie between Rubbermaid and Iris. Out of the 3, Iris is the easiest to clean and they don't discontinue/change sizes constantly.