I always make them research planets. I play in a gigantic galaxy. If there was a shortage of planets (i.e. tiny gal with all players), it might become a factory world.

An entertainment facility so they don't lower my overall tax bracket, and either two factories or a factory and a lab.

What good is a Factory without a Starport? Other than building, well, buildings . . . which you can't fit too many of on a small planet.

What good is a Factory without a Starport? Other than building, well, buildings . . . which you can't fit too many of on a small planet.

If you dont have a factory on say a class 4 planet than even if you focus on social production it will take something like 100 weeks just to build one entertainment center. And then when the building upgrades become available it will take forever again to get them. And dont worry about wasting space with a factory because it will probably be constantly working on some social project untill they are all upgraded all the way. By the time you have habitat improvement or terraforming you can either build a starport or when you are done building on the extra spaces just build something else over the factory.

All labs.

Factories and a starport. I Use it to pump out constructors or other small ships throughout the game.

I concur, factories and a starport. PQ4's make nice troop farms for your transports, since they hit the pop cap anyway.

Another trick I do: don't develop them at all. In the initial colonization phase, the low-PQ planets can serve as a buffer, to make the AI will colonize them instead of the high-PQ planets you really want. But if you wind up colonizing them anyway, you can plant a very small population and then trade/gift it to an AI. You'll only get around 80bc for it (less than even the price of the colony ship), but it will be a real drain on his economy. Better his than yours. And later (after he's developed it) you can flip it.

P.S. I think it might have been me who suggested earlier to put a farm, an ent. ctr and a market place on a PQ4 planet. That was wrong. Won't work.

I'm a stickler for neat borders and territories, so I prefer not to let the enemy take it. Besides, supposing they have Mars, for example, means they've got the range to get not just to, but past your homeworld. I prefer to site a Factory and three labs on the planet, since the population limit keeps it from becoming an effective tax farm and the lack of space curtails the number of factories that can be built on them.

I buy either 2 research and 1 market or 1 research and 2 market, depending on how I feel at the time

I tend to ignore colonising Mars, let the AI have it, then watch it revolt under the sway of my influence capital.

1 factory, rest labs.
After I get final science building built (neutrality center or discovery spheres), I replace last factory with another science building.

No need for entertainment centers, even if I tax high, sicne I use races with morale picks and build trade goods that increase morale.