Which choices have you never made?

I've just activated Legion and this made me wonder - who sold Legion to Cerberus? Whether we play parangon or renegade, there is no point in doing that. Same for Grunt: what would be the point of discarding allies for a dangerous mission where every talent should be used?

This made me realize that despite playing multiple playthroughs over the years, both parangon and renegade, there are some choices I've never made, in spite of wanting to explore the games' variations. For instance, I 've never chosen Udina as councilor at the end of Mass Effect 1 because he's being a dick no matter what and becoming councilor during the third game anyway.