I made a blueberry melomel, which spawned my Levitating Blueberries question not too long ago, mostly due to slight off-notes likely from minor oxidation. This happened from the plastic, solid carboy cap having a hairline crack around the hole where the air-lock was. Now, with the same batch I've gotten another defective cap issue. Another crack, this time around the top thread of the cap.

I have a couple of rubber stoppers that I haven't used yet, any feedback on their pros and cons versus those of the plastic/solid ones? I'm so sick of the shoddy quality of these plastic ones failing on me.