As a long time Sierra fan I personally would say
Quest for Glory that one is the easiest to get into, there's less dead ends puzzles are pretty good and are normally based on your character and their skill set, this series in my opinion is the lest punishing of the Sierra "Quest" games
Now for a secondary choice it would be either Police Quest or Space Quest, Know SQ 1 and 2 hadn't quite aged that well they defiantly had aged better gameplay and frustration wise then King's quests though they do have some wtf moments, like Slot's o' Death and the glass shard you don't know about unless you type the command to look in the right spot, same with the emergency survival kit in SQ1. But it's humor more then makes up for it.
But of all else I say avoid King's Quest unless you don't mind a really rough game especially 1-3, King's Quest had some of the most ridicules puzzles ever and plenty of dead ends and in 1 most of them were just random for example: there's a Dwarf that will appear at random and steal items from you the kicker is he can also steal the three key items that are needed to win the game and there is no way of getting them back. Then there's the "Rumplestiltskin" Puzzle this along with the Snake in KQ2 are probably the worst.
So in KQ 1you meet a old Gnome and you have to guess his name so you think "Rumplestiltskin" nope, so you find a clue that says "it pays to think backwards" so you would think his name backwards right? Nope again the solution is the name Rumplestilskin written in a backwards alphabet meaning instead of starting with A you start with Z. then there is the Snake puzzle in 2 where in order to get this important item you need to somehow figure out that by throwing a saddle at a killer snake will turn it into a winged horse that will give you the item that will help you enter the castle. Oh and you can die randomly in both 1 and 2, walk into grannies house will either give you granny or the wolf you don't know which as it's random.
I wish I was kidding but I'm not and don't get me started on KQ5's Yeti puzzle. The only KQ I still can play is 6 which to this day is a amazing Adventure game.