Most of the alternatives have one thing in common; for each sequel added the game quality gets worse.
I give my vote to Space Quest, only because of the great humour in it.
In general, I have some kind of love/hate feelings about the Sierra games. Most of the time I enjoyed playing them, but they have a bunch of really annoying features.
As an example I remember playing Larry 2, standing on the top of the volcano in the last part of the game. It was obvious what you had to do to complete the game, but... wait... how do I lit this darn molotov cocktail... I have no matches!!!! When was my last save....?
Those of you that have played the game may remember that the matches had to be found BEFORE you left the boat. All my save games were from the island.... [Restart game? Y/N]