CDR audio have a data header already written on the disk I believe which specifies that they are to be used exclusively for audio use- These are the only disks that dedicated audio burners can use, as they are programmed to check that this header is there. Data CDR's lack this header, and can be burnt to any kind of cd so long as they are made using a data cd burner (IE cd writer drive in a PC). The simple reason is that on Audio CDRs (as well as blank tapes and minidiscs and other dedicated audio recording media) you are paying an additional fee that goes to the music industry- presumably in order to compensate for any piracy that goes on with them.
With Data CDR's you are not paying any such tariff and as such they are cheaper. There is no reason why an audio CDR should sound any better than a data cdr of equivalent quality (which will be cheaper).
CDR' s rarely sound any different between brands, although i have noticed that on one of my cd players it likes the cdr's burnt at a lower speed. Any differences between sound quality on different quality cdr's will usually be a result of your cd players laser focal length not suiting the cheap cdr's. Although if you can hear the difference by all means buy better cdrs. You should only buy audio cd-r's if you have a dedicated audio cd burning deck. Otherwise you are wasting your money giving it to record companies- this is why i would always recommend getting a cd writer drive for your pc rather than a deck for your hi fi.