If you’re used to buying single trip Metcard tickets (including 5x daily / 10x 2 hour), stick with Metcard. Not having to touch off at the end of each journey, there’s no chance of being charged a default dare, and you wont have to be one of those awkward people holding everyone up when exiting their suburban station. Also, we wont mention the overcharging that occurs using myki money, which is not an issue with the Metcard system.
If you are someone that uses a fixed term pass, there’s some advantages to using a myki pass. If you lose a Metcard pass, you’re out of pocket for the remaining balance of days. Using a registered myki, your replacement card will have the remaining balance of your pass transferred to it. The other main advantage is that the myki smartcard is more durable than a paper ticket, meaning that you can avoid the problems of bent Metcard tickets not validating in machines.