IMHO Erwin is much easier to use. However, it doesn't support the logical level as well as Designer and it doesn't support the application level at all. But on the physical level there it's robust and much easier to use than Designer. They're really different animals. Designer is an Information Engineering workbench (or it likes to think that it is) while Erwin is ment for supporting the physical implementation of an already designed database. Of course, I haven't used Erwin in the last 3 years so later editions may change the feature set. Your milage may vary.