I think the discussion about whether Delta has better forecasts of turbulence than the competition are directly relevant to OP’s decision on which of the airline options you listed they should book. Delta claims they have better turbulence avoidance solutions than other airlines, which is a debatable claim with both pro and con arguments. Delta also marketed the A220 with references to this solution, so discussion of whether the A220’s version is different than other aircraft is equally relevant, IMHO.

Also, once OP’s flight is booked, turbulence forecasts available to the public can still be helpful for a fearful flyer to know what to expect on their flight, even if there aren’t a lot of alternate options. Also, keep in mind that if weather is severe enough, there may also be a weather waiver that would allow for routing changes without a penalty.