I love Sierra game, and I collect in them too
Lucas made really really cool adventure games, but they didn't make so many, while sierra, might have made some crueler looking games, but I like the stories, and I think they made so many that you can be entertained for a long time.
Then (from a collectors point of view) the sierra box where very cool, with some interesting booklets and other stuff in, while (those lucas games I got) is more ordinary.
I love my sierra collection, and still try to expand it
then sierra released one of the best games ever (Half Life