So where should the tubes be?

Preamp or phono stage.

Where tubes make the biggest impact on the sound is the amplifier.  But, good tube amplifiers also represent the highest cost in making a switch (good output transformers are particularly expensive and important to the sound), so that might not be where one would start.  Also, the matching of a tube amplifier to the speaker is critically important, so you will need to either have some experience or some help in that area (e.g., a good dealer).

I can’t speak for anyone else, but for me:
in the past.

I have an all tube system now—preamplifier, phono preamp, DAC, and amp.  It sounds super. 
Only downside is diagnosing where the “bad tube” is when it happens. It’s 25 total tubes!  Better than it has been here but still lots of tubes to roll and monitor!  

I prefer them in the pre and phono stage at minimum but extend it into amps with speakers that mate.

The only thing I don't like about tubes is the generalizing characteristics the unwashed put forth as fact ...
Tubes are still a very good choice to appreciate the music end of it that most fire bottle users focus on.
I left tubes when I had a slew of little ones with curious minds and hands. When I slowly got back into tubes again I realize now I stopped the revolving door that SS brought. Just my experience, not an enditemant  on SS as both can mimic the other to some margin. For me, for whatever reason others may claim for me, I simply find the music for tone and timbre more real to my ears and how my bit of grey matter deciphered it all.