The Biggest Decisions of Mass Effect 3

For a summary of the choices we've made during the Mass Effect series and how they'll most likely affect the unfolding story in Mass Effect 3, you need not look further than captainstarball. Here's your sampling:
The Quarian War - In Mass Effect 2, you encounter the flotilla during your loyalty mission with Tali. The Quarians are restless with the travel and wish to retake the homeworld. You can use Shepard's persuasive charm to either convince the Quarians to abstain or go to war. If you convince them to war with the Geth, it is likely that you will lose the military support of the Quarian and possibly the Geth. If you told them to abstain, you may have the entire flotilla at your disposal.

The Collector's Base Both Mass Effect titles have ended with a big decision. The one to save the crippled Collector base for research or to destroy it may have been the biggest decision yet. The choice to save the base may arm humanity as well as the rest of the galaxy with new weapons and an understanding of the Reapers and their technology. However, this could backfire and possibly mind control hundreds of thousands of humans. To destroy the base is safer but could potentially leave the universe at a disadvantage when the Reapers come calling.