I like building colony ships that can be built in 1 turn in the later stages of the game. A colony ship with Ion Engine IIIs and a Solar Sail III moves 8 costs around 4650 (or so) minerals, which can easily be built at any planet with HI, 120% construction aptidude, SY III and a decent amount of population. Medium or Large Transports can bring in the population after the colony is established, so why bother having huge, expensive colony ships?
