What is the most important component to consider while building a new system?

I’m with Atmasphere and chorus. 

Except, of course, stating the obvious, if one does not have speakers or 'phones, then THEY are the most important.  :)

Over and out.

I am mainly in "the source" camp, but also a strong believer in system/room integration, which has to do with the speakers/amps match as well as the room. I also agree with priority to good electricity. If I could design a sound room and system today, I might start from a different proposition, maybe speakers rather than source. But my system has evolved based on existing rooms. My main strategy has been to invest mostly in the source, and then, into the best preamp, amp and speakers. Why?  Because, unless you have a good source, you will never be sure what the components further down the chain are doing - or not doing. 

i would add further that i disagree with folks who say it is the source... that’s silly because it is all important, it is after all a signal CHAIN

what must be primarily considered is which component has the most impact on the actual sound being produced in the room, and that is always the speaker -- the physical transducer that actually translates the electrical signal back into something we actually hear

speakers, even very good ones, have the widest range of sonic differences (or some would say, the greatest variability of amplitude and nature of distortion from an idealized musical signal being sent to them)... and the speakers’ dispersion pattern interacts intimately with the room they live in and the listening position - so this is by far the greatest variable - by far

not that the source isn’t important... it is absolutely important... but you put up 5 $5000 sources versus 5 $5000 speakers in a given room, the speakers will provide the greatest differences in what the setup will actually sound like

There is no question that speakers are central to the SQ.
However, the source can make or break a system. I once heard a million dollar system with a very digital edgy sounding CD player and I wanted to run out of the room screaming!
When I got my long searched for Woodsong Garrard 301, I wound up upgrading every part of my system. Only now do I have a destination rig. And the greatest and most significant upgrades were to my front end-TT, arm, cartridge and preamp with phono stage.
Garbage in, garbage out! Great “food”, great “meal”!

Another way of view: The order of cost for each component from most expensive to least expensive.
1. Speaker
2. Amp (power + pre)
3. Source (turntable/CD player)
4. Cables
That is how I spent for my components.