I learned how to type and how to spell by playing Space Quest 3. ( "MOM!!!! HOW DO YOU SPELL WARP MOTIVATOR????" )
It's hard to pick a favorite... and this might be an unpopular opinion, but MAN I really enjoyed SQ5.
Space Quest 3 was my favorite of the series - followed closely by Space Quest 4 (which is ironic, as I tend to dislike time travel type stories) - but since this poked fun at it - and also had a guest appearance of the Energizer Bunny (which for some reason I've always been obsessed with) - it was super enjoyable! Also the foreshadowing of Roger having a son!