SQL & PL/SQL

Hi ....
Assume that a user contains the whole data schema of an application...(user db_user... let's name it)....
Also all other dbusers corresponding to application users do not have any db object.... the simply be granted to use the db objects via objects grants and public synonyms.....

Which is the best approach.....(regarding the performace , security , e.t.c. )
1) the dbusers which are app. users simultaneously to access the db objects via public synonyms and grants or,
2) use the "alter session set current_schema=db_user" and appropriate grants of course to to access the db objects .....?????

Many thanks...
Sim