Yeah... this is a scary one... On the surface the Bootstrap4Xpages project is the clear winner. The resource aggregation.. It uses build in renderes... so it performs much better overall then if you did it manually.
The problem is there's one 1-2 people working on it that I know of. So I worry about it keeping up with newer versions and everything. I'd love to help that project but don't have those skills.
If you use pure bootstrap.. then things like dialogboxes... and re-styling things like pagers become a much bigger chore to deal with.
Nothings ever easy...