Do you start fine tuning the system with cables or tubes ?

Tubes make the bigger difference IF your cables reveal them. The wrong cables might obscure them. It's that old synergy thing again. 

@hilde45 - what they said.

Respectfully disagree.

The thread is implicitly treating tubes and cables as equivalent variables, but they aren't on the same footing. Tube differences are mechanistically grounded — different tubes measurably alter harmonic distortion profiles, output impedance, and noise floors. You can predict and measure the consequences. Cable differences are far harder to demonstrate under controlled conditions, and the evidence for audible differences beyond basic engineering thresholds is thin. That asymmetry seems worth naming before comparing their relative effects. 

This is also a good example of where purely subjective discussion starts to spin its wheels. Nobody here is wrong exactly — everyone is reporting genuine impressions from their own systems. But without some measurement grounding, the opinions just ping-pong indefinitely, each one canceling the next. Measurements don't resolve everything, but they at least give the conversation something solid to push against.

And as someone noted earlier — room acoustics outweighs both, which is probably where the conversation should start.

I find for me it’s tubes. Especially 

the input tube of my amp and the output/

gainstage tube of my pre. 

However getting a bit off topic here, the biggest improvement

SQ wise for me was when my amp and pre-amp were re-capped.