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I post this comparison not as a contest between the two singers, but rather for informative purposes.

Both recordings were done under the Victor/HMV label:

McCormack's was recorded on 7 January 1910.

Caruso's was recorded on 26 November 1911.

It is interesting I think, to compare acoustic recordings of a spinto vs. a lyric voice.

My own analysis: the recording seems to capture Caruso's overtones better, but since we have no idea what kind of overtones he had in real life it is difficult to know for certain. All lyric tenors seem to have a similar sound when recorded on acoustic (compare McCormack with Gigli and Schipa here), although you can still distinguish them by their singing style, mannerisms, and the slight amounts of overtones which ARE captured.

On another note: In my opinion the best Caruso recording of 'Una furtiva' was the 1904 with piano. As far as his voice is concerned however, I would say Caruso's prime was in the years between 1906 and 1915, give or take a year or two. So 1911 would fall right into that time frame. He sounds fantastic here (despite the quality of the record).