Phono Stage, Tonearm, Cartridge Question - Which is the most important?

I would say phono stage. To get the best from a cartridge you need a great tonearm. To get the most from a tonearm you need a great table. From a table, a phono.

But cartridges wear out fast. Tonearms don't. Tables don't. Phono stages don't. So if you are considering cost, get a great phono stage first. For example, I had a Rega 3 back when - sounded good for the day. With an ARC SP8, the system sang.

I had planned to buy forever speakers that day - Magnepan Tympani IVA. But the SP8 made more difference, so that's what I bought. YMMV

In very Basic Terms a Phonostage receives Signal that is generated by the Interface of the Styli being in contact with the Groove and the Styli’s having LP Groove Modulation pass it, the undulations of the modulation are creating oscillation, which is transferred via the Cantilever / Armature into the Coils where the oscillation becomes a minuscule electrical Signal.

Note: Ambient Energies within the Listening Environment are able to be transferred to the LP Groove, resulting in a influence on the oscillation being produced by the Styli’s contact within the Groove. Contaminated Grooves also have the potential to influence the oscillation being produced.

The more faithful - unadulterated (not influenced by ambient conditions) the energy being generated and transferred from within the Groove as a Signal to the Phonostage. The more accurate a representation the Signal will be, when the transferred signal’s Gain is Increased by the Phonostage. It is not uncommon for a MC Cart’s Signal to be increased by a 1000x, which will be ideal for the next stage of amplification.

A Phonostage is Typically a tool to increase Voltage and carry out correction to RIAA.

RIAA is way to complex for myself, the Link will help if wanted to be looked into further.

What I am sure of over many years being a Vinyl Source Enthusiast and meeting with many who are similarly passionate through social interaction, is that Phonostages are not all viewed equally.

A Phonostages capability is as important to some as their most valued LP Pressings. Not everybody wants the same thing sonically from a Phonostage, in the same way not every bodies most valued LP Pressing is to be the same.

https://en.wikipedia.org/wiki/RIAA_equalization

In relation to the follow up inquiry about which is having the most impact on the sound.

I stand by the suggestion that a LP Sources Trilogy of Supporting Ancillaries, mounted on to a optimised support structure, will produce sonic far from what could imagine achievable. 

My take on it, is that expensive equipment required for Vinyl Replays, is being used to its least advantageous/ sold short, if not mounted on a optimised support structure.

I strongly suggest not spending too much money of any ancillaries seen to be an upgrade until the Support for the Trilogy of Ancillaries is addressed.

Ask anybody on any Forum would they revert back to former mounting methods used for the TT, after having discovered something perceived as optimised, the chances of getting a 'Yes' would be a hard find.  

If you can answer us this question, we can perhaps begin to answer yours: are your upper teeth or your lower teeth more important for chewing?

I stand by the suggestion that a LP Sources Trilogy of Supporting Ancillaries, mounted on to a optimised support structure, will produce sonic far from what could imagine achievable.

What does it even mean?

Being a manufacturer the phono stage is the most important.  We have access to so much equipment and the phono stage is what produces the sound.  You don't have to spend big bucks on a cartridge like the Denon DH103 and get a wood body for that, or a TT.  We have used older modified TT's with good wood surrounds and that will compete with most anything out there.

Happy Listening.