In Sydney threads: "We should have a zone system like Melbourne's."
In Melbourne threads: "We should have a distance system like Sydney's."
The grass is always greener ........
There is no perfect system. What we have are systems with greater and lesser capabilities and functionality. The argument is as much around the system back-end as the customer interface.
Each user will have their own preferences. Some might benefit from a time-based system alone with multi-modal functionality and unlimited transfers. Melbourne offers that; Sydney does not.
Some other will benefit from a distance-based fares structure which does not usually include multimodal facilities. Sydney offers this; Melbourne does not.
If every journey combination possible on a system were to be stored in the database and charged individually (as for example occurred under "paper" ticketing with Edmonson cards) then as things stand each individual point of contact - tap on / tap off by whatever jargon - will likely take a lot longer. It is in everyone's interests to minimise that time.
London has what has been described as the "Rolls Royce" system when compared with Melbourne's "Rusty Holden Ute" but has sill chosen to reduce the complexity of the fares structure to a manageable level. Graduated fares based entirely on distance have been replaced with six zones for most rail operations and at first four, then three, then four, then two for bus travel which is now at a standard fare irrespective of distance and time. Bus routes are however generally much shorter than they were perhaps 25 years ago as the traditional lengthy cross-town routes have been broken into sections to improve reliability.
So while Londoners enjoy a mostly user-friendly system (not glitch-free but pretty good) they don't always benefit from distance-based fares. The daily cap applies just as it does in Melbourne and is easily reached on a simple round-trip commute. London has not lost sight of its tourists and occasional visitors and retains the paper-issue daily Travelcard available at all tube and suburban rail stations; they have never been sold on buses.
What system would I use were I in charge? That depends on which location we are talking about. But for Melbourne I would offer a smart card electronic system which does not require the user to rent ("buy" is a misnomer - you don't own the card) the card first. That would sit alongside and be fully interfaced with the ability to purchase cash fares from bus drivers with a single-use non-transferable paper ticket, likewise for trains (sold from vending machines at unstaffed locations) and similarly with trams where a fairly simple coin-slot machine on board could issue paper single-trip tickets and possibly give change as well. Bus and tram single-use tickets would be valid for one trip to the end of the journey irrespective of distance; train tickets for a maximum of 2 hours from time of issue.
That doesn't open the floodgates for the train tickets to be abused as unlimited-travel passes as all stations could be fitted with entry / exit gates; once the user left the station the gate would retain the ticket. End of journey. But two hours would have to be allowed to take account of the maximum cross-city travel time for example Pakenham - Sunbury. The train tickets would be priced accordingly at a higher rate than bus or tram ones.
The smart card would operate on a combination of distance and time charged accordingly and with a daily cap set at the level of a return trip by train from the farthest suburban station to the City and back. That also allows for an element of off-peak pricing as a tag on - tag off within the specified hours would be picked up and charged accordingly.