Well as per title: I am always directly opening with 2 science buildings. And maybe even 4? Just to get that first tech out of the way? (Banking or experimentation).
This leaves me with few ships for scouting resources though, so am wondering: do you still think this is a good start? In a “netural” situation where you are not sure yet if you are landlocked or have aggressive neighbours.
Default for what size game?
In a 64p I’ll tend to go 3 - or 2 if there are some good stars in sight that are close so that I can get to 4 or 5 quickly.
Starting with 3 raising to 4-5 (depends on timing) means you can usually get your first tech before 2nd production. If that’s banking, experimentation or weapons this can lead to a strong early lead that if you time will you can push forward. Choice may depend on wider landscape.