it depends more on the overall quality of the cable than the shape of it.
You can take a good cable that transfers data well, and make it into a round cable, and it will STILL transfer data well.
Or take a crappy cable that transfers slow, and after rounding it'll still suck.
But if you compare the quality flat cables with the poor quality rounded ones, it would seem that rounded cables suck! This is what many of the websites that review such things are doing. Plus, with round cables being so popular, companies are trying to score a fast buck by making them very cheaply.
In otherwords- get round ones if you want, just don't skimp on them. There is no performance difference inherent in the shape of the cables.
I have my doubts that round cables always help with airflow anyways. I have a harder time in my case that has round cables tucking them away. My other machine (built by voodoo pc) is so tidy with the ribbon cables that sometimes you wonder if stuff is even plugged in.
When I build systems now I try to mimic some of the techiniques in my voodoo case and it works pretty good. A ribbon flat against some portion of the case is not going to restrict airflow at all...
Hey the Coolermaster rounded cables are bad ***. Very high quality. They have a twisted construction with pull tabs on the ends and are extremely flexible. Once you get rounded cables you will never go back, even cheap ones. The only problem with the Coolermaster's are they do not come in a bunch of colors. They look really cool and it does not take a brain surgeon to figure out they they are better for air flow. If you have say a Raid 0+1 setup with CDRW and DVD CDROM, floppy, etc., you can end up with a real rat's nest. For the little ole change it takes to get them and the way they look it is a no-brainer.
I'm cheap. Rounded cables cost like $12+ for a system. It'll cost you less than half that for ribbon cables (compgeeks). They work the same, you know? It's kind of crazy from a utilitarian standpoint to put 4 fans in a case and think that rounded cables are going to make an appreciable difference in cooling.
That said, round cables do look cooler! Unfortunately nobody comes and looks at my case but me, so it would be kind of useless for me to spend the extra $!
I only use round cable because the extra layer of protection makes it hard for the cable to get cut. I keep them out of the way of my ducted cooling system so their airflow benefits are negligable.
Flat cables are alot easier to hide away if you know what you're doing and take your time. But they're alot easier to kill. Really small systems can't accomodate the bulkier rounded cables so you're limited to folding and snaking the flat ones.
It's a mixed bag really. Their benefits depend on your usage.
Everyone is right. Round cables can and sometimes do suck. Flat cables will always out perform round cables because cross-talk is minimized. If you have airflow problems you can use round cables or even better, get a full tower and flat cables won't make any difference in the airflow because of the increase volume.
I have rounded cables and they rock, I bought em at Sidewinder Computers and they are the coolest. They're copper colored. I bought em because it cleaned up the interior of my case and besides, I like having copper looking tubing running through my computer. Reminds me of my truck kinda.....Anyways.