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

I believe the weakest link in my system is the speakers which are causing me issues with inconsistencies whenever I play them i.e. they sound good one day and not so great the next.
That can't be the speakers, unless your moving them around, or they are Electrostatics with dynamic bass drivers, as the ESL's can be less efficient on very humid days compared to dry days and with a dynamic bass driver the whole speaker can sound bass heavy on humid days and visa versa on dry days.

If none of these apply to you then it's your electronic chain (source to amp/s) that is your problem.

Cheers George   
I started with speakers . Because everyone has something to hook to them. And sources can be half arsed while you get a feel for your room. Once you are convinced you are committed and can afford it . Get the best amplifier just above your budget , play with that a while and feel the G’s of having control of your speakers for the first time . then get a preamp you definitely cannot afford. And you are rockin. In that order. 
And also , do your research be in love with what you are getting before you even get it. Everybody is upgrade upgrade upgrade . Can you imagine the system youd have if you did waste money upgrading on half measures? .blah . 
Speakers do not change dramatically from day to day. If they seem to sound that different day to day, then there is something wrong with your system, that is, the components. 
Get the best sounding speakers you can afford first.