Kraftmaid isn't all that great of a brand:
The fronts and drawers are nice, but the cabinet side panels, backs and shelves are just particleboard with a laminate finish unless you upgrade to the top-level all-plywood construction.
http://kraftmaidspec.com/whykm/index.cfm?navigationid=13300
Omega appears to be better since they use all plywood cases:
http://www.omegacab.com/constructionDetails.asp
As far as KD cabinets - you need to look at the specifics to compare the quality of materials. The most common KD cabinets are IKEA: they're all particleboard cases (and many fronts are just veneered particleboard as well)