what is more important ?

Hiya ,

Just wanted some views/opinions on what is the most important piece of equipment in the reproduction of sound/music.

I know and have heard that the dimensions of the room has the biggest impact but what about the speakers, amplification, and source... which one would give the biggest sonic differences(for better or worst) if replaced ?
If my current system needs upgrading which part of the chain should I focus on first to get the best 'bang for my bucks' ?

Cheers all

First: speakers quality improved by the necessary tweaks...

Second:   room treatment...(absorption and reflection panels, Helmholtz resonators,Schumann generators...)

Third : amplifier and dac  tweaked...

Fourth : Last but not least at all, tweaks and cleaning about mechanical vibrations, and the  electro-magnetic grid of the room and the house...

My experience is contrary to many people : Buy good products but dont focus on pricey one at all; the most important fact for audio is not the price/ quality value of your gear but the way you install and implemented them in your room...The most astounding upgrade comes from that, not buying anything more costly...

I tend to agree with the speaker-first camp but I've also used a cost-balanced approach to very good effect. As an example, say $1000 each for an integrated amp, source(s), and a pair of loudspeakers, throw in a modest amount for cables and you can have a nice sounding system with no glaring deficiencies. Plenty of research and careful matching is a must, of course. 
Other ways to think about upgrades.. Lost of little upgrades...Particularly works well if you buy used gear. New not so good as one is constantly losing money ..Or, buying one really good bit of gear every few years.. Gradually bringing the entire system up. 
Lots of folks say start with the speakers, get the best you can. The other way to do it is buy the best source you can... When I watched "The Audiophiliac" YouTube video on his own system, I was struck at his sources. $18000 a pop. vs the rest of the system. Other 'nice' stuff, but not like his sources.  Anf he has been around.. Having been a salesman at Sound By Singer..

Millercarbon- amen!
I don’t always agree with you, but you hit the nail on the head. A very large part of the hi-fi listening experience is subjective. As I have heard the saying before, “We do not see what is in front of our eyes, we see what is behind them”. That saying holds true for one’s hearing and “perception” of what was heard.
The recipe for best results first shot:

1) Speakers first (taking room into consideration when choosing).
2) Then carefully match the amp that is capable of driving the speakers well.
3) Then match pre-amp to amp carefully as well, if separate.
4) Then top it off with good quality source gear of your choosing. If phono, make sure phono matches to phono stage of amp/pre-amp carefully as well.
5) Tweaks that might help: a) power conditioning, b} speaker placement, c) physical separation/isolation of components from each other (avoid stacking on on another), d) wires (need to be good quality, not expensive, Mogami is a very safe fallback for modest cost), e) also isolate speakers from suspended floors as needed to avoid interactions that muddy the bass and obscure the mid-range

You can start with an amp if you want but that will mean some speakers that might work best otherwise may not be driven well to the max.