For pure self defence. Go krav maga, or find a good reality based self defense (RBSD)school.In sydney, try Flora fighting system, budo jitsu, join a good martial arts forum like Blitzmag.net to ask for something near you.
The thing with RSBD is that they go beyond the phyiscal part of confrontation. they look at psychological (huge part) as well and go beyond physical mpvements in the air.
Things like scenario training, weapons defence, tactics, etc...
If your serious about self-defence dont waste your time on trditional stuff like karate. For pure fighting techquies, extreme power, fitness, conditioning look no further than the proven arts of Muay thai, boxing, wreslting, BJJ, Sambo and combination of two or more of those will be Mixed martial arts. And the best way to find a good MMA , muay thai, boxing , wrestling gym is to look at the fighters they've produced. The proof is in the pudding.
SYDNEY gyms: Elite fight gym, bulldog gym, sinosic perosh, roots, gracie barra, gracie Oceania, ultimate fighting arts.