The Ordinary Caffeine Serum vs Mandelic Acid, which one should i buy?

I'm a student, so my sleep schedule isn't the best and I get dark circles every now and then, and when I'm really tired I also notice a bit of puffiness and these tiny festoon like lines under my eyes.

I'm debating between The Ordinary Caffeine Solution and Mandelic Acid, but I'm mainly trying to improve my under-eyes.

If you've used either, did you notice a difference? Or is there something else that worked better?