For me..

1) St George Budapest 1971-74
They won everything from GFs to winning the Interstate Championship beating all 4 Melbourne teams, to winning International Tournament in Japan beating the hosts as well as a leading Danish team Frem 3-0
To having half the Socceroos in a successful FIFA World Cup Qualifying campaign through Asia that includes Israel and NZ.
Special memories 

2. Brisbane Roar 2010-12
2 GF wins in front of over 50,000 fans including  one of which was the greatest GF ever played.
36 game unbeaten run
Thomas Broich…
Super Quality

3. Melbourne Victory 2006-07

A joy to watch Fred, Thompson with 15 goals
Averaged 30,000 per game
Won the GF 6-0 in front of 55,000…with Fred providing 5 assists for Archie
A super team…