ah yes, the age old question:
vs 
To actually answer your question (Since she has since convinced me to play some LucasArts games), I'm honestly torn. I think generally Sierra has puzzle design that's more accessible from moment-to-moment, whereas I do feel like LucasArts is responsible for more of the truly headscratching combination puzzles (I'm slowly making my way through Grim Fandango right now actually and DANG there's some abstruse stuff in there)
On the other paw, Sierra is prone to plenty of 'screw you' design things that are pretty infuriating in their own ways; I think unkindly of the MULTIPLE reflex tests in Space Quest 4 for instance, and just the presence of deaths (gotcha and otherwise) in general.
@indi honestly- as a person who prefers Sierra- Sierra games have a lot more bad puzzle designs. Gabriel Knight 3 and Codename: Iceman are two of the worst offenders I can think of off the top of my head
I don't know if I'd call Sierra more accessible, but yea, Lucasarts does tend towards a little more zany puzzle solutions
@vahnj Yeah, that's a fair point! (Also, huge bonus point to you, I totally forgot Codename: Iceman even existed) Accessible is probably not the right word, I think Sierra's bad about scattering stuff all over and backtracking and gotchas, but LucasArts is more prone to very poorly telegraphed adventure-game-logic as far as getting past particular points. Or maybe I'm just really annoyed at Grim Fandango right now. ;)
@vahnj Elaborating on this, I don't think "You can't die" actually has any effect at all on difficulty; for all it removes specific gotchas and forced reloads, it does at least allow you to narrow the solution-space sometimes. Banging your head against the same three screens for hours with zero feedback is intensely annoying in its own way.
