Nope, although it depends on what you mean by 'best'. If you have ten labs, two equal-RP projects, and two scientists (each with 20% bonus and the ability to control ten labs) it will take the same total amount of time to research both projects however you split up the labs, but if you do all ten labs on one 'til it's finished then all ten on the other, for half the time you'll have one project already finished. That may not make much difference if your two projects are BFC Speed and BFC Range, but if they're a pair of missiles you can be manufacturing one that much sooner, and if they're increased mining & increased production, that's a lot of output you'd be missing out on.
Which means it's highly dependent on what you're researching, how many scientists you have vs how many labs, whether their bonuses are in the right field, and how many small projects you have lined up. And it changes everytime you build a new lab, recruit a new scientist, or a scientist increases her abilities.