ur mum
No, seriously:
1- Either JLA or Avengers. What's important here is that I got help from anyone of them: Superman, Wonder Woman, Martian Manhunter, Green Lantern, Captain Marvel, Thor or Hulk. So I don't care about the team, I just need a "planet crushing" arms. Also, Fantastic Four could do the trick: Richards probably knew that a comet the size of Texas was coming, so he might already have a raygun to save us.
2- JLA, Avengers or X-Men could do the trick: each time have adventages, but the best would probably the JLA, with their incredible versatility. Manhunter, Frost and/or Charles Xavier would be the most important dudes on the field. Also, Fantastic Four could do the trick: Richards probably knew that a space invasion was coming, so he might already have called the Silver Surfer to save us.
3- Holy shit. Here, we are in troubles. I call JLA, Avengers and X-Men. If they gang bang Darkseid first, then Thanos, we might have a chance, but the casualities will be in the roof. Also, Fantastic Four could do the trick: Richards probably knew that Darkseid and Thanos were coming, so he might already have called Galactus or built a raygun save us.