- People who can easily continue to guard against significant COVID risks for several weeks without much downside other than quality of life should wait several weeks for Pfizer or Moderna.
- (People who have to expose themselves to a non-trivial amount of COVID risk no matter what should take the J&J vaccine if they'd have to wait several more weeks for Pfizer / Moderna. I haven't run the numbers on this, but at some point I'd expect the additional risk exposure from being unvaccinated for several weeks to outweigh the difference in efficacy.)
1. Moderna and Pfizer provide significantly better protection against non-severe infections.
- J&J provides:
- 28 days after the injection: 66% protection against moderate to severe COVID infections (72% "in the United States", but I don't know to what extent that is robust to further spread of foreign variants in the US) and 85% against severe disease 
- 48 days after the injection: 100% protection against severe COVID. (I don't know what 100% protection means, exactly - a commenter pointed out that there is no such thing as 100% protection - but for the sake of argument, let's say it's close to that.) 
- Moderna and Pfizer provided 94.1% and 95% protection against any symptomatic infections generally after the 2nd dose 
2. I'd expect that even non-severe infections increase your risk of long-term lingering effects (in addition to being fairly unpleasant in the meantime, but I'm less concerned about that).
- I don't have great evidence for #2 yet. While mild infections have a non-trivial risk of long COVID , it seems like even initially asymptomatic cases account for about a 3rd of long-COVID cases . I would hypothesize that the risk of long COVID is significantly less for asymptomatic cases than for symptomatic cases, but haven't researched that much yet.
Zvi said in his 2/4 COVID post, "I’d pay a substantial amount to get Pfizer or Moderna instead of J&J if I could get either one today, but given the choice between waiting and taking what’s available, I will happily accept the J&J vaccine now rather than hold out for Pfizer or Moderna."
What am I missing? Is this just a difference in the weight we place on resuming higher-risk activities sooner rather than later? Or am I overplaying the superior efficacy of the Pfizer and Moderna vaccines?