This was one of my favorite games as a kid and I still have love for it.
I went back to both of them, decades years later, and found Last Crusade to be much more challenging in a way that games no longer offer (besides Dark Souls) -- they let you make mistakes which hinder or make completion almost impossible. You could get pretty far in to Last Crusade and not have the required items to progress further.
This was in contrast with Sierra Online's adventures, which had plenty of surprise deaths and deadend situations. This led to saving frantically at every step, which isn't particularly fun.
I loved Sierra games -- the first three EGA Space Quest games are my favorites -- but I see the point of avoiding player frustration.