none of the above.
The decision that took me the longest was the side quest in ME 1 on the citidel concerning the unborn child who could have a crippling life long deisease, for which there is treatment, but there is also a genetic alteration treatment, (with a low chacnce of doing something WORSE) that would prevent it. I actually had to stop and seriusly weigh both sides for a couple of hours. I got off the game and asked a couple of people their view on it. Eventually I sided with the 'go for the gene treatment.' option because I would never want to inflict avoidable harm on someone that lasts their entire lifetime. Of course, there is a risk, there is risk in any action, and inaction is an action of its own.
In comparison, the Rachni,the reaper base, and a couple of others were easy decisions. (I actually CHANGED my decision on Garrus's loyality mission in ME2, because fuck it, if it was me, I would kill that guy by inches!) The geth problem was intresting, but it was 'ensalve or destroy' and my stance on that was long ago decided in favor of destroy. The genophage cure was a pretty impressive one, but ultimately I couldn't deny them the data, however horribly it was attained. ( I have benifited in real life from medical advances based on Natzi experiemental data from the holocaust, and would be a hypocrit to deny that to others. My paragon sheppard would deny it, but I the person would not. Thats why I have a renegade, a paragon, and a 'if it was my decision' save.) oh, and FETH THE COUNCIL! I WARNED THEM!