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

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. 

Room acoustics is top priority. Unless that’s shorted out you are not really hearing the potential of your components. 
Properly treated room will also reveal differences between cables, tubes and even masters of the same album much easier. It will reveal any inconsistency in performance of your tubed equipment on a day to day basis. You will be rolling tubes endlessly because tubes will be the first thing you will always suspect when the system sounds off. Eventually you will go on to listening to your equipment and what the tubes are doing instead of listening to music.
You will accumulate a large collection of tubes that’s worth half of what you spent on them initially. With today’s prices on vacuum tubes having 3-4 complete sets of tubes for VAC Avatar SE is about $3,000 - $4,000 for the modest non NOS  nothing fancy tubes. Before you know it, you will be thinking that spending this much to upgrade my table or cartridge or get an awesome phono stage would make so much more sense…but you’re stuck with tubes, looking at bias meters and scratching your head trying to figure out which tubes are contributing to the issue you’re troubleshooting. That’s a ton of fun and man does that add to the overall enjoyment of the hobby! 

Re room acoustics, agree with speaker systems, but don't forget headphone and nearfield systems. The most dramatic change for me was with a Woo WA2SE headphone amp going from stock to WE422. A clear quality improvement. Also rolled the AU7-style tubes on the WA2, but much less of a difference; more flavor than quality.

I am not a pathological roller. Did a bit of experimentation early on (5-6 years ago) since then have not bothered re-checking. Rather enjoy the music.

+10 on the room priority but sometimes that isn't easy, or quick. So assuming you have decent cables, tubes can make a big difference especially in source components. But, I'm referring to going from low-cost, new tubes often supplied with new gear, to well chosen NOS (in my experience).