Any of those products will allow you to document at an extremely low level of granularity.
Haven’t used Designer since 6i (the previous version), but it is strongest for “traditional” data modelers (using information engineering approach) deploying to an Oracle DBMS. It’s absolutely brilliant. I especially liked the stored procedure generation aspects and CRUD matrices.
However, its not an ideal cross-platform tool. ErWin or PowerDesigner will handle multiple platforms more readily.
Reverse engineering and generation should excel on all the products.
I’m currently using PowerDesigner 10 on a SQL Server backend and am sufficiently happy with it. If you want a variety of modeling tools (ERD, UML, BPM) in one box, it does a decent job.
I’d strongly recommend downloading demos of all of them (which should be available), exploring ease of use, and trying them out against some test schemas.
None of them are cheap, so playing with them upfront will be worthwhile.