The main trail up Mt Ainslie is 4.2km return and ~300m elevation on mostly paved track with segments of stairs and single track.
On a Saturday morning around 9am, I encountered about 30 other walkers, runners and boot camp participants.
Good quality track with decent views over Canberra, including towards Black Mountain and to Parliament House. The sound of traffic is never too far away though, so it is not as ideal as the Hall to One Tree Hill Lookout or Mt Taylor trails.
View from Mt Ainslie toward Black Mountain, Canberra