I used FS2002 a fair bit while doing an IMC rating* here in the UK. While I never found it useful (or even fun!) for VFR work, setting the weather to a 500-foot overcast made it a very useful for IFR practice and i'd recommend it quite highly. The biggest problem I had was with the controls; I could never get my joystick (MS Sidewinder) configured well, so the aeroplane was always much too sensitive in pitch. Flyable, but a bit frustrating.
I haven't used X-plane, but it has got a very good reputation. Don't know anything about the Jeppesen simulator.
Another very good bit of software for learning IFR flying is
RANT. It's not a flight sim as such, but a way of learning how to interpret the needles while flying IFR procedures (holds, precision and non-precision approaches, DME arcs and all that good stuff). If you're already familiar with all that then it's not necessary, but if you're learning then it's very good. Paid for itself many times over when I was training - much easier to learn on the computer than at £2 per minute in the air
* as you're in Oz and may not know, an IMC rating is a bit like a subset of an IR, with reduced, but still quite generous, IFR privileges (edited 'cos I can't spell!)