If it’s about saving money on family holidays, then the points redemption opportunities may also be relevant. Reasonably easy to attain given the CC climate in the US.
No idea about DL but ime FB is actually quite good at this, especially also for partner rewards (eg domestic Delta). Also has quite different ticket conditions.

as for IRROPS, customer service itself is also pretty important. Again, no idea about KE or DL but cultural differences and quality are a thing here. E.g. KL tends to be quite pragmatic, whereas I
found another non-skyteam airline absolutely impossible to deal with