Balanced or RCA?

For 1.5 metre cable between ARC LS-25 and Bryston 7B STs would it be better to get a balanced cable or use a plain RCA cable? I am no believer in magic cables, so what I am now looking at getting is a pair of Kimber Hero balanced 1.5 metre.
For that length either is fine. Balanced sounds much better between my amp and preamp.
I agree with Phil that for a 1.5 meter length, either the RCA or balanced cable should be fine. The primary advantage to balanced cables is noise reduction when you have a long run (such as in recording studios). I have used both balanced and RCA 1.0 meter interconnects between my Bryston SP-1 pre/pro and Bryston power amps, and frankly can't hear any difference the two. I ultimately opted for RCA, since they are generally less expensive than balanced, thereby allowing me to get a better quality cable. I have owned Kimber Heros, and think they are one of the two best interconnects in their general price range (the other is Alpha-Core Goertz TQ2, which replaced my Kimber Heros).
You may want to contact both manufacturers, some manufacturers specifically design their gear for one or the other (yet offering both), therefore giving a greater result. I have asked several manufacturers this question and they have always told me what would give the best results.
Assuming your equipment has both balanced and RCA connections, I suggest you borrow one of each cable type and listen. You need to let your ears decide what sounds better in your system and your room. In my case, I decided to go with the balanced connections because it sounded better (IMHO). I have a Rowland Concentra I integrated amplifier and the Meridian 508.24 cd player. Balanced connections are more expensive so this option will cost you more money. Some audio equipment is not really balanced so you also need to check this. Good luck. cheers...
Balanced is better from my experience. I tried the 1.5m RCA and balanced XLR versions of the Transparent Music Link Super XL interconnects between my Krell KRC-3 preamp and Mark Levinson 331 power amp. The balanced XLR version was more transparent, open, neutral, airy, dynamic with more harmonic integrity. The improvement in my setup was quite dramatic. I chose the balanced XLR.
XLR offers you dynamic sonic performance whereas RCA offer you less in resolution but smooth sonic quality. It all depends on your personal taste. My opinion is:

XLR, for syphomy, complex music
RCA, vocal, string or simple music
It depends. I own both balanced and single-ended editions of otherwise identical interconnect, in two different cable types, all of which are 1m length. Between my internally-balanced DAC and my internally-balanced preamp, there's no question in my mind that going balanced makes a small but musically worthwhile improvement, at least in my system. I tested this by doing both hook-ups simultaneously and switching between them instantaneously via the remote from the listening chair with the relative volume levels preprogrammed to match. In audiophile shorthand, the balanced connection lends the music a distinct bit more 'palpable presence' - in other words, it sounds a little closer to life than it does via the single-ended connection, presumably because it's slightly less degraded along the way, and because the connected balanced circuits can function differentially without the interposing of lossy adaptors or phase-splitting stages.

On the other hand, between the aforementioned internally-balanced preamp and my non-balanced power amps, there seems to be a slight loss switching to a balanced interconnect. This may not be too surprising, since it was predicted by the amps' manufacturer, but of course I felt the need to find out for myself anyway. I would not characterize the difference as being quite as meaningful (in the other direction) as was the improvement from source to preamp, which makes sense as it probably only has to do with the balanced input signal's being routed through a bit of extra contacts/solder joints/wire on its way to ending up at the same place and in the same form as a single-ended input is from the start, with no other theoretical advantages accruing to the single-ended connection.

These results lead me to two tentative, anecdotally-supported conclusions: 1) Short wire runs are no reason to automatically dismiss balanced connection in lieu of direct experimentation; 2) Whether or not the sending and receiving circuits involved are truly balanced, rather than simply providing XLR connection to a single-ended circuit for convenience's sake, will have a lot to do with the existence of any potential upside. And then there's the issue of the wire itself - from what I understand, a lot of interconnect models (including the ones I used) are internally no different between the balanced and unbalanced versions except for their termination, but not all, and it stands to reason that if you're talking about one of those models that's actually differently constructed for each version, then all bets would be off.
In lieu of some responses, I would like to elaborate further on what I had stated; some manufacturers design their gear in manner whereby it will benefit one over the other, although they offer both RCA and XLR; therefore it isn't that the cable (type) is better but rather it is a better match for the design.

One person above mentioned Meridian, due to their design, they will tell you that XLR should give you best results with their gear.
Cheapskate that I am, I went to the local musical instrument emporium and bought two Digiflex cables with Neutrik connectors. I am tempted to say that the sound is better using these inexpensive cables with the balanced connections on the LS 25 and Bryston 7B STs than the Blue Heavens with the RCAs. Go figure. This set me back a whopping $41.29 CAD, all taxes included, with no waiting time! "It will have to do, until something better comes along", with apologies to that great lyricist.
Score! (I've heard that expression used in hockey games.) Good for you - count one for our north-of-the-border audio skeptic. More money left over for poutine, eh?... ;^)
Depends on the equipment. In many cases RCA is just fine for short cables.