ICS seems to be emerging as the dominant Spaceship strategy, and the Liberty tree is a crucial part of that.
For a conquest win on pangaea/smaller/more open maps, a Horseman rush is faster. Honor & Tradition are helpful.
If you want a Cultural win, the Liberty tree is not that beneficial. Piety & Freedom are more important.
If you are on a larger/continents/archipelago/highlands maps, a combination of Horseman rush + ICS will probably be the fastest. Some tradeoffs will be necessary between the two.