Soy isoflavone aglycones are absorbed faster and in higher amounts than their glucosides in humans.

By T. Izumi, M. Piskuła, Sachiko Osawa, A. Obata, K. Tobe, M. Saito, S. Kataoka, Y. Kubota, M. Kikuchi. Journal of NutriLife, 2000

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Bioavailability and bioefficacy of polyphenols in humans. I. Review of 97 bioavailability studies. (2005, background): “Izumi et al (110) found greater bioavailability of aglycones, on the basis of Cmax, but they did not measure isoflavone concentrations between 6 and 24 h, whereas Setchell et al (112) reported that the mean time to reach Cmax was prolonged to 9 h after glycoside ingestion.”
Evidence for lack of absorption of soy isoflavone glycosides in humans, supporting the crucial role of intestinal metabolism for bioavailability. (2002, background): “Some absorption of aglycones, but not -glycosides, was shown to take place in the rat stomach (51), and if this is true for humans it would contribute to the faster absorption rates of aglycones than of -glycosides (24, 30).”
Bioavailability and bioefficacy of polyphenols in humans. II. Review of 93 intervention studies. (2005, background): “After 4 wk of 30 mg/d isoflavones, the peak plasma concentrations showed no significant changes at the measurement times of 2 and 4 wk (111), which indicates that the bioavailability of isoflavones does not decrease during long periods of intake.”
Polyphenols: food sources and bioavailability. (2004, background): “However, in another human study, peak plasma concentrations were markedly higher after aglycone ingestion than after glucoside ingestion, and this effect was observed with low or high single doses and after long-term intakes (102).”