Scratch

I had trouble deciding at one point whether to save the Quarians or the Geth, I found out if you save the Quarians Legion tries to kill you and your saved by Tali and you eventually kill Legion. If you save the Geth you have another chance to stop the upload and if you have high enough paragon or renegade you can force the fleet back and save them both but if  you continue the upload the Geth join your army but Tali and the rest of the Quarians die unless you stop Tali from jumping off the cliff. So if that helps because I spent a long time trying to figure out what do to. If you have any more questions just leave a comment below.