“What medication is best for stress?”

I'm not a big believer or advocate of medication for stress--which is different from anxiety. There are medications for the latter such as an SSRI  (i.e. Lexipro, Zoloft, etc.) or a Benzodiazepine such as Xanax, Klonopin, etc. Stress requires an overall life management change including time, stress, emotional and physical management (i.e. exercise, nutrition, etc.) along with the creation of life balance.
Psychotherapy would be a sound idea to achieve this.

You have a lot of natural remedies like bacopa, gelsemium and coffea cruda.The last two are homeopathic medicines with no side effects or interactions.The first is a complex of herbs to stabilize your mood and anxiety.

See this link...
https://www.healthline.com/health/anxiety-drugs
or
https://www.mentalhelp.net/stress/reduction/medication/