What is the order of importance of the parts of an analogue rig?

@sokogear : "  What about SUTs (set up transformers). Should that be a separate category for those with MC cartridges? "

it depends on the Phono stage design. Some designs has not enough gain and the designer opted by a passive gain stage through an internal SUT other designers opted by active high gain stage that does not needs a SUT and the stand alone SUT normally is used with Phono stages that handled only MM cartridges.

Even there are gentlemans that own an active high gain Phono stage and listen their LOMC cartridges through an stand alone SUT and this means that the cartridge signal will be added with several kind of developed distortions ( every kind of. ) for the use of additional IC cables between the Phono stage and the external SUT. 
Now the cartridge signal must travel for a half cable or 1m. cable that degrades the signal an exposes the signal to RFI, EMI, external vibrations, etc, etc. and not only that but the cartridge signal must pass through additional RCA/XLR input connectors and solder points adding more degradation and what happens at the Phono stage input connectors is duplicated at the SUT output connectors too. Along all those the cartridge signal must pass several meters of wire in the SUT internal transformers.

That's why : ""   that were trans-formative to the performance. ""

As an active high gain stage the passive SUT/stage can be addictive but certainly different.

R.

1) Tonearm/Turntable (equally important, should be well-matched so they work together2) Phonostage3) Cartridge (but must match tonearm effective mass, and the better the tip and coils, the better off you are)

In the end, all three or four of these things should be well-matched, and in the same category of quality, so one or more of the components aren't being bottle-necked by the better component[s].

@sokogear - there are a couple of things I consider very Important in an analogue setup using a Rega TT...

I guess this could be considered part of the Tone Arm, but the "method" attaching the TT to the phono stage - i.e. "the interconnect".

You can have either...-
1. a single cable run of quality wires from the cartridge to the phono stage
2. what appears to be a single cable run, but is in fact a different cable that is joined to the tonearm wire (e.g. as on my old RB240 arm)
3. RCA sockets + separate interconnect.

I’ve only experienced #1 and #2, but #1 is my preference to date and resulted in significant improvements in sound quality - together with selecting quality RCA plugs.

#3 can be a great option if you are auditioning Interconnects, but requires exceptional cables to come close to #1

Better still - I upgraded to an Audiomods Tonearm (perfect for Rega TT’s) and have never looked back - It came with a high quality one piece harness (i.e. #1) and great RCA plugs. It really highlights cartridge performance in some exceptional ways.

My next choice that I consider almost as important would be Phono Stage - I used budget phono’s (i.e. < $400) for many years - stepping up to a better performing phono stage did a couple of things...
1. improved sound quality greatly
2. it is compatible with a larger selection of both MC and MM carts
3. it is really quiet - no hum

Other more minor things that I have found that contributed to better analogue sound quality on a Rega TT include
- a metal sub-platter
- an acrylic platter
- a ceramic bearing
- a Michell Technoweight - a counter balance weight that lowers the center of gravity of the weight to the level of stylus
- a substantial (i.e. heavy) plinth - once you have experienced a plinth with mass you will not go back.

With the above items addressed, you will get the better performance out of any cartridge you choose.

But in general - I echo most of the other posts - in that everything across the entire system is important - especially cables

Regards - Steve