Well I know you have an upside to the bridge. I put mine upside down to see if it would work and it didn't. But the bridge has no indications of which side is up or down. Concerning the SLI connectors themselves, I just use the first one from the left and it works for me. But I suppose either one would work, though I never tried it.
If you're new at the SLI setup, make sure your motherboard doesn't have any jumpers on it to lock SLI out like mine did. Also, make sure to enable SLI in the bios.