And, with Alzheimers, he might have gone through grief and panic multiple times.

there isn’t a “best” really. Depends on your wants/needs.

for true Openness, I don’t think anything beats a Voron.
Prusa is great (good track record, good support, Hardware is not open anymore though, can work out of the box), but expensive.
plenty of others get you something largely decent for low prices (qidi, creality for example) but long term support seems likely to lack, and there are always reports of some issues for some and great results for others.