What is the most important cable?

In a two channel system what is the most important, and, is it best to have brand synergy?
Only you can make that decision. Depends on your gear, ears, and room. By brand synergy, do you mean all the same brand cables? If that is the case, once again, it all depends on your ears, room, and gear. If you want to tweak the system, you may have more than one brand.

If, by brand synergy, you mean one particular brand of cables mating well with one brand of electronics, I think all audiophiles want synergy between cables and components.
I was told the source. But I would think the speaker my resonong is that everything runs throught the speaker all your sources. From what I read keeping the cable all the same brand doesn't matter because each cable handles a specific need but I would keep the tupes the same. For example audioquest doesn't play nice with Kimber since audioquest is a solid core and kimber is not.

Me I use all the same. Or trying to.
I would say from the cd player to your pre or amp would be the most important to begin with........
The next step up.
put your most refining cable from pre to amp
put your most natural sounding cable from cd to pre
experiment a lot, synergy synergy synergy

that stated I use Acoustic Zen Matrix from cd,phono out, et
and Straight Wire Crescendo betweeen pre and power amp
I have Harmonic Tech Pro 9's bired to the speakers (haven't upgraded yet but these have killer depth, imaging, resolution.
Good question. A local tech that makes cables told me today that he feels the preamp power cable is the most important for the power cable, but I found that the amp power cable makes the biggest difference in my system to my ears.

Happy Listening.
The one that your dog just chewed up :-)
Amp for power would be the most important especally tubes this is because the amps sraw the most power and amplify the most noise.
cd to preamp ic
Mine is the most important cable.

I hardly care at all about yours.

(speaker cable)
i noticed the biggest difference between cd-preamp....i think.......wait.......im not sure i can tell the difference between anything anymore.
IC's - Source to pre-amp. If you don't get all of the info right from the start, you won't have it at the end.

Power Cable - Amp, like someone else said, it draws the most power and amplifies the most noise.

This is exactly what I experienced in my system.
the one from the brain to the ear canal
The first one in the signal path..
Amp ----> Speaker