I'll start off by listing mine:
The T-800, Terminator 2: "I know now why you cry, but it's something that I can never do." Gets me every damn time.
ADA, Zone of the Enders: I think I'm the only one who played this game more than the MGS2 demo that came with it. I will never not laugh at the exchange of "You may speak like a human, but you're still a heartless computer, aren't you?" "That is correct. What is the problem?"
Codsworth, Fallout 4: He survives the nuclear holocaust despite not having a bunker and waits 200 years for you to come back. When you look at what changes his relationship with you, he mostly just wants you to be nice to people. I never swapped him out as my companion.
B.O.Y.D., Ducktales 2017: He's adorable. 'nuff said.
Oh yeah, the Quarians have genocidal intentions. I just kind of remember them getting over it in the "best ending". I'm not sure I ever did that though. I either sided with the Geth or Quarians and wiped one or the other out.
Whether or not the Quarians or the Geth wipe the other out is largely decided on if you choose to save, like, a single fleet admiral.