I think Atletico are slighty favorites, but reality is that both Atletico and United are having very difficult seasons.
Atletico needs new blood.
Their team is aging, has few young talent, lacks back-up specially in attack and Simeone's tactics are insufficient to compete in Europe and now against Madrid in la Liga. They managed to become Spanish champions last season although with a lot of difficulties towards the 2nd half of last season. Those troubles, like the vulnerability in their defense, are still ongoing and I don't think Simeone will be able to correct them in the middle of this season. Unless he changes his dull 4-4-2 or finds a pearl within his academy that can replace Felipe and Giménez I think their best result will be to finish 2nd or 3rd place in La Liga. Maybe they are able to beat United, but won't compete in Europe against Chelsea or Bayern.
As for United, Ragnick seems like a capable manager, but he doesn't give me the impression to become an instant hit like Tuchel did with Chelsea. He was semi-retired and has no PL experience.
First, he should be aware of United's fragility in defense, which will take a long term to repair. Secondly, he still needs to implement his game tactics under this squad. Third, he should prioritize game quality over results in the short term.
Fortunately for him, maybe Atletico are the perfect example to put into practice his development with this team. Surely they are better option than PSG.
Lastly, Cristiano is Atletico's worst nightmare.
In the end, I don't think any of these teams will land in the SF. Both are weak, mentally, and underdeveloped.