Acid bath.
It just makes everything melt away.
Cold shower to wake me up in the morning. Nothing better.
Suna ofc. I don't know why would you answer anything else as a Finn. Note, you usually take showers before and after anyway. For shower I prefer mild or even cold shower during summer.
I use a sauna almost everyday. 10-15 minutes and if i'm running really hot i take a cold shawer.
Baths for relaxing but shower first ^^
nanobots to remove grime and dead skin.
Don't think you can really even compare these to each other since they are all meant for different purposes. Shower is what you do to wash yourself and you are not supposed to go to a bath or a sauna without taking a shower before and after.
Out of these three I like sauna the most for relaxation though.