I'll be in Sydney next week from Monday to Saturday. I'll be doing some tourist stuff, visiting friends, some who are central, others in the suburbs. What is probably going to be my best option for transport, and what ticket options are likely to be suitable for this situation?
There's pretty much just one, the MyMulti. You'll want to buy a week long one for your trip, about the only question is which zones to get. The zones only apply to trains (all buses and ferries are covered), so just look up where all your friends live and buy the one that covers it. That said, I'd almost be tempted to say you should get a MyMulti3 no matter what - it's only $17 more than the central zone one, and lets you visit the blue mountains and the beaches to the south and north.
Unfortunately, at the moment Sydney doesn't have any sort of smartcard based system for public transport ticketing. The MyMulti day pass is very expensive (it's about half the cost of a week one!), but if you're going to be in the city for at least a few days and you want to get around lots, it's the ideal choice. I think it's something like 3 return ferry trips on the Manly-Circular Quay route and the weekly pass has paid for itself, so you'll find it cheaper very quickly!
The only slight thing to be aware of is that the MyMulti ticket has a surcharge to use the airport stations, which is quite substantial. If you have a MyMulti ticket, you can however take the 400 bus from the airport to the nearest non airport line station, which doesn't need the surcharge.