|Who will you choose?|
In the end there can only be one. Either the Quarians or the Geth. So who will you destroy and who will you save? Both have huge fleets and technical expertise to help you construct the Crucible.
You choice either kills Tali and the Quarians or Legion and the Geth. So EA/Bioware does allow to you choose the fate of an entire race.
Ultimately it doesn’t really matter who you chose. Whichever you choose will commit their fleet to your war effort and use their engineering skills to assist with the construction of the Crucible.