for me having played the majority of Sierra adventure games from childhood to now I have to say while both the early King's Quests and Space Quests haven't aged too well I have to say that Space Quest was a better series over all, now don't get me wrong I like KQ but man that series was evil and in my opinion the only one that a non-sierra fan or KQ fan will like is 6 which was a amazing game because it had such a great team working on it plus the story was written by Jane Jensen who later brought us Gabriel Knight 1-3.
but save for 6 Kings Quest is usually riddled with puzzles that are quite illogical i.e. toss a saddle or bridle on a snake to turn it into a horse with no clue that is the solution also another example is the old gnome in 1 where you have to guess his name which you would think was Rumplestiltskin but no so you may find a clue telling you to "think backwards" so you think the name backwards but again you would be wrong it's the name spelled out in a backwards Alphebet Z-A rather then A-Z, cheap deaths but that's most sierra games, and tons of dead ends especially in 1-3 which is really bad in 1 and 2 since often you have no way of keeping yourself from being put in a unwinable state as at random you may run into a little gnome or thief that will steal from you and can steal the three items needed to win the game(what he steals is random) and if he spawns next to you as you enter a screen guess what your screwed.
While Space Quest 1 and 2 had their flaws and you can dead end yourself it's no where near as bad as most KQ's, though for players who grew up on older adventures it's a bit harder to dead end yourself, at least in my opnion anyway. Since it's usually because you forgot to take everything not nailed down or search everything before leaving a room with the exception of the glass peice in 1 and the survial kit but if you typed look before leaving the pod you will know the kit is there. But again they do have their faults for example in 1 there's the slots of death mini game which will kill you at random so it's a case of spin, save, spin, save, spin, and save and 2 there's that annoying Alien parody that gives you a game over but it wont happen for a few minutes so you run the risk of saving the game thinking nothing is going to happen and will be unable to finish.
So yeah I say SQ