Hydraulic levelers usually have a bit more range (extend further), so they can handle a more uneven site. The ability to manually set the individual legs (which most hydraulics controllers offer) can also let you handle odd shaped surfaces a bit better. But if you always use parks that have reasonably well-prepared sites, there really isn't any significant difference.
I gather that air or air + hydraulic also costs more, since it only seems to be available on high end models.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL