[Suicide Junkie]

Consider the number of nearby planets too, and don't worry too much about the slow build time.

If you don't have many colonizable worlds in your homesystem, then you'll probably want to go with the faster colony ships.
If you've got 5 or more colonizable worlds, then with the 1-turn colony ships, you'll have your homesystem colonized in the first year, PLUS a bunch more colony ships exploring through the closest warppoints.

You may want to slip a fast 1-turn scoutship into the mix, to peek in the neightbouring systems, and keep your slower colony ships from exploring dead-ends.