PHAs are slightly less sensitising on skin, making them more suitable for sensitive skin. Polyhydroxy acids may also act as antioxidants and have shown to improve the skin barrier's strength. Having said that, all exfoliating acids work by removing dead skin cell on the stratum corneum, they need to used with caution to avoid inflammation or over sensitisation of the skin. 

See also:
Gluconolactone
Lactobionic Acid
Antioxidant
Alpha Hydroxy Acid