Seagull will work best for you if you are an intermediate PHP developer with at least 1-2 years experience and a good exposure to OO concepts.
Less experienced users should also be able to use only the admin screens to manage the data in an app once it's setup, without knowledge of the internals.
Installation is very easy:
Using the web-based installer: your server environment will automatically be detected and you will be prompted for a few basic details while the installer creates the schema and populates it with some default data. The installer is a 5 screen wizard and is designed so you cannot progress if you supply erroneous information, ie, incorrect DB login credentials.