For me;
S.P.E.C.I.A.L: Agility - because I like to be sneaky and guns is by far my favorite weapon class. I also use VATS almost all the time, so this is essential.
Skill: Speech - because I really enjoy getting everything out of the story and speech opens up so many options.
Also guys, give a reason for your choice (:
And, yes I failed at spelling SPECIAL.