If Bioware ever decides to choose a canon ending for Mass Effect 3, which one would you prefer?

I'm still learning my way with the forum, didn't saw your response earlier.

I dislike Rannoch arch for this very reason: why is "jesus Shepard" responsible for the peace or extinction of quarians or geth?
The result would be more believable if it was like the SM, depending of Shepard's actions the result would be open war, peace or a agreement between them.
The quarian admirals even acknowledge the information you bring from the geth hub is disturbing or contradicting their belifs, but ultimately this don't have a influence at all in the outcome apart from some war assets.

The result is always war between them and Shepard step in and save the day or kill a entire race. WTF?

Is like the suicide mission in ME2, I really don't understand how people loose squadmates in the final mission.
I think the best part of the argument is... because Miranda.
Who don't remember the pointless arguments about her because she has sex appeal, inteligence and well... she's perfect (she's genetic tailored after all).
She's also a fairly common character to be honest, but this is irrelevant.

But more important, regarding tactical and missions decisions, if you follow her advice usually you end with no squadmates casualities at all.
For f*** sake, you have to send a TECH in a tube, but instead you send a scientist, like Mordin? Or better yet, Jacob, a special ops soldier?
What are the odds they end dead, hun?

As the decision to exterminate one of them, I never have to face it in most of my playthroughs, only when I deliberately sabotage myself.
If you really think about it, give me one logical reason for letting Tali or Legion die in ME2? Or kill them? Just one.
Sure, they could have been a casuality in the SM, but again, only if you rush or didn't planned the mission well.
Or we could be narrow, shallow and ultimately DUMB and let Cerberus get Legion "for studies".

And we end in a loop back to the start about why is Shepard deciding to kill or save a race.
The jesus Shepard.

As for people favoring genocide or extermination? Don't know.
Hate? Prejudice? Lack of information and knowledge? Blindness justification based on science, ideology or religion?
In ME1 we have to deal with a trade negotiator complaint because his substitute is having the nerve to actually TALK with the salarians regarding trade agreements and trying to reach a deal that would satisfy both parts.
Shepard is a "alien loving scum", do you remember?

Comparing ME with real life is also not a good thing, because is frightening what Bioware think politics are.

 But what about Tali?
Even if she's not an admiral and being exiled, you need to have her present to the mission success, otherwise you are screwed no matter what you did before.

This is completely falsue.  There is absolutely nothing stopping Shepard from siding with one or the other even when both Tali and Legion are present and his/her reputation bar is as full as possible at that point in the game.  Siding with one or the other will result in the annihilation of the other side.  The player simple has to make the dialogue choices that correspond to siding with whichever side they want to survive.  Saving both is what requires both Tali and Legion to be present and a reputation score that is high enough to unlock those options... but you certainly do not have to save both even if you can.

As for the difference in the reputation points you receive at that stage for each action. consult the morality guide in the Wiki.

masseffect.wikia.com/wiki/Morality_Guide_(Mass_Effect_3)?action=edit&section=14

You'll be very surprised to learn that for the entirety of the Priority: Rannoch mission a total of 2 reputation points are awarded... and those two points are awarded regardless of the decision you make... you need only talk to the Geth VI or Tali.  There are a number of paragon and renegade and reputation points available during the Rannoch arc... but the vast, vast majority of those are associated with the side missions you do before the actually Priority: Rannoch mission (i.e. Perseus Veil, Geth Dreadnought, Admiral Koris, and Geth Squadrons).

Sure, but like you said, if you want to choose between the two.

I have a pure paragon playthrough like this BTW: Legion and Tali are alive, Tali is exiled, I solved their loyalty argument in ME2 amicably and I rewrited the heretic geth in ME2.
After performing the missions in Rannoch arc by saving admiral Koris and shuting down the geth fighters, I was able to broke a peace betweeen them (contrary to what the ME wiki says).
My reputation bar was almost full if memory serves and only the paragon choice was available.

I would take the "Reject all choices" option. It essentially creates a clean slate so you do not have to worry about continuity.

I like the destroy ending. We can hear about how the Quarian and Turians starved to death on the long voyage home. One the weirdo planet, Garuss killed Tali and ate her so he could hold out until search & rescue showed up. He did not want to, but she was having an allergic reaction and could not be saved.

Liking for the Dr. Strangelove gif.

I guess I'll vote destroy as it is in the game *shrug*. Though, in terms of the epilogue in Extended Cut, I thought Shepard's monologue was pretty cool in Control which is why I like to pick it. I'm shallow like that.

Or do you think that without the reapers it is possible to rebuild the relay rings?