As much as I can afford it during a long and vigorous Colony rush, I set aside 2 or 3 citizens as government scientists. When I am convinced I have found the best Research world and gotten the hub buildings up, they move there and stay there. 90% boost on a hub world is impressive! I make sure to park the right Mercs there and everything. If my gang of leaders is working Research as well, it gets even better.
On a truly large map with a truly large empire, the 3% does really add up, but my feeling is that if you are at the stage where 3% counts because you have so many planets, then 6% is even better. So, I go for Leaders a lot. They are also good if you are conquering your way to a giant empire. Instant bonuses to new planets is very helpful to a rampaging tyrant.
Still, pumping up an early Research planet with some planted scientists is going to pay off all game long. And it is more important as your initial ratio of planets per player from map settings goes down.
So many choices.