I (and most php professionals) recommend switching to PDO, because:
- it can do everything mysqli can do too, and more
- it has a far better error handling (option to use exceptions)
- it has the advantage to switch the database driver if needed. So if you need to switch from MySQL to Oracle, MS SQL, PostgreSQL, SQLite, ..., you can do this with a minimum of changes
- it can use named parameters
- It has an OOP syntax only
But the syntax of PDO is more different to mysql than mysqli is
If your question is, if you have to change to provide your application is running even on future php versions, than the answer is yes. You only need to choose which one you prefer.