In a very simplistic way:

- Smoking brings cancer and damages lungs.

- Vaping damages lungs (more research needed on other possible conditions).

- Nicotine pouches damage teeth.

I suppose the healthiest way of ingesting nicotine would be nicotine pills, which exist to help people quit smoking (and which is why they are very expensive).

People that I have seen substitute with vaping seem to get more addicted to that.