I have thought about this a few times
The type of seal used (double lip seal with garter spring) is usually fitted in "one way" applications i.e. stopping the oil pissing out around a rotary shaft of a gearbox but in the wheel bearing situation we want it to work both ways, keep the grease in and the shit out.
Perhaps one should consider which of those we want it to achieve most efficiently and fit the spring to the "pressure side" So, if you jet wash your bike every day or spend most of your time riding along in rivers, fit the seal with the spring outermost. Otherwise, not.
Of course, logic would also say that by keeping nice clean grease in, we're keeping the crap out.
My conclusion would be that it probably doesn't really make that much difference either way. (but I always fit mine spring innermost)
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