ISS for the reason that scientists giving production and engineers giving science is amazing in-and-of-itself regardless of going for a science victory.
ISS is absolutely worthless for a planned strategy. It requires Satellites, that is far too late. If you are going for Space Victory, you will get to this tech first to grab Hubble. This is last place where you get GS, so after it's build, you pop all your saved Einsteins and use up your faith for rest. That alone is usually enough to bulb yourself through most required techs and you should win within 10-15 turns.
Meanwhile, to get ISS project, you need to wait for current proposal to finish (can take up to 20 turns), then be one of two civs to propose it, then wait 10 turns (I believe) to get it to voting stage, pass it, then focus all your cities for production and hope for best (as in, if runaway Civ decide it's worthwhile to go for it you might not even get it).
The only time I ever would see it useful if you can propose new resolution within ~5 turns of you just getting Satellites or if you haven't been actually planning for SV before.