This is purely subjective. Some people prefer the simplicity of my_object=something
then just fetching it using objectmap.get('my_object')
while others, prefer using objects in Java. e.g. using LoginPage.TXT_USERNAME
Depending on your personal preference, and philosophies, you should determine which way is easier to you.
Personally, I think using java page objects are much more efficient because of the auto-complete that eclipse provides. I could do
LoginPage.TXT_USERNAME
LoginPage.TXT_PASSWORD
instead of having the possibilty of misspelling your object if you use a properties file like this:
objectmap.getProperty('TXT_USRNAME') # oops! forgot the E, and i wouldn't've known it until runtime.