Balanced or single ended leads from your arm.

If your phono preamp (or phonostage in your main preamp) accepts balanced inputs, then by all means use them. Not so much for hum and RFI resistance (good cable shielding and proper grounding should take care of that) but because a MC cartridge is a balanced output device anyway (as you noted) and will basically produce more (effective) output into a balanced phono preamp circuit. The net effect of this increased efficiency is a lower noise floor (or better signal-to-noise ratio.)

As for the idea that a balanced IC in this application will allow the use of longer tonearm cables to the head amp, I'd be careful making that assumption. You need to be more concerned with increased resistance, inductance, and time smear that accumulates as even the best cables get longer. Remember, we're talking here about the tiny currents produced by phono cartridges, not the ones coming out of your preamp to drive your amp, so the difference between a one meter tonearm cable and a three meter tonearm cable can be significant. That's why the audio industry standard for tonearm cables has, for a long time, been 1.2 meters or about 4 feet.

Most phono preamps/stages I know of that are balanced input design are quite expensive. Remember also that they will (if they're stand-alone phono preamps) have balanced outputs, so you better have a main preamp with balanced inputs!
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The Aesthetix Io phono stage has balanced (and RCA) input jacks so I rewired my Walker Proscenium with cryo treated XLR's in place of factory RCA's to take advantage. The result was a nice improvement.

Even if a phono does not offer full balanced input, if the XLR jacks are provided the superior contact area and connection is worthy of consideration.

Personally I prefer the Swiss XLR's constructed with gold over copper pins and finished in black. The brand is Neutrik (same as provided on the Io and Callisto).

What you prefer Swiss cables over the Purist? Blasphemy!:-)

Hi, I really can't add any more input to the above posters other than I have had very similar experiences. My BAT VKP10SE Superpak has both RCA and XLR inputs. The XLR's yield a little more gain, lower noise floor. The result is that the imaging and detail is better. It's pretty noticable, not small imo.

Good luck...

Ken,
My experience has been that RFI can be significantly reduced by going with balanced cables from the table to the phono stage. In my case, 1000ft. from a large radio tower, RFI is a significant issue, that led me to abandoning many a single-ended preamp. Balanced cables was the single best way to eliminate my RFI problem.
FWIW, any VPI owners out there, you can buy a balanced junction box for $150 directly from VPI that replaces the box on any JMW arm. Yes, a high price for a little metal box with two output jacks, but well worth it for the sanity it provides.
The Neutriks that Albert mentions are by far the pro audio standard, they're cheap & easy to find.
RFI issues aside, I agree w/the other posters that balanced will provide an overall lower noise floor. Go for it! Cheers,
Spencer