Hi ausnat. Welcome to AFF!
With JQ star class you will get a Millenium Business Class seat (the same used on QF domestic services) and a basic meals and alcohol service (pretty average). You also get a portable AVOD kit and a comfort pack.
With BA WT+, you get an Economy seat (a little wider and a better pitch) but the seat won't be as spacious as if you were in the Millenium seat. I'm pretty sure the meals on BA WT+ are just economy so nothing special there.
Also, BA WT+ earns Full Economy SC's while JQ *Class will earn Business status credits.
If you live in MEL, I woud go for Jet* on the direct flight. If you live in SYD, I would take BA. It's only a 9hr flight which will go by pretty quickly anyway.