I think StoredProcedures are better for maintainability because they can create a clear interface to the database, Stored Procedures are going to have better performance for complicated queries, this is because when you store the procedure the DB has the opportunity to compile the procedure in advance, with parametrized queries it need to be compiled every time it is run.
Simple applications that use parameterized queries might very well perform as well as an equivalent application written using stored procedure; but as the application grows in complexity and needs to scale, stored procedures offer the best solution for growing and maintaining a robust, scalable, enterprise-level application.