Usually it's more efficient to produce Wealth because that will allow you to up the research slider and since you most cases will have more science multipliers, you will get more
However, if for some reason you have more gold multipliers, build Research.
Short, simple, correct. Go with this.
If for some reason you DO manage to have more gold multipliers (this is quite rare), then build research. However, the science buildings are cheaper and prioritized more in games where the outcome is in doubt, so almost always you'll want to build wealth to push the slider.
Best is keeping the slider at 0 while building science buildings then bumping it up. I usually only build wealth when:
1) I'm out of things to build -----> typically a hammer city and I'm in a period of the game where I've locked diplo to such an extent I don't need units (!). You need to know your stuff to skimp on units though.
2) Desperation warmonger capturing of 15 cities by the early ADs. Building wealth in such a scenario is inefficient, but it's a heck of a lot better than striking and getting owned by itty bitty crap civs when you have no units. If you don't have currency, extort alphabet from somebody and build research your way to currency (and possibly CoL).