which one would be the best one to get first??

im at level 20 if that helps...

Well, that really depends on your character. What SPECIAL? What fighting style?

S:8
P:5
E:7
C:5
I:7
A:4
L:5

fighting style??, um guns etc

Well, i meant do you run in guns blazing, or take the silent approach? Basicly what skills you use for fighting?

Intelligence if you want more skillpoints. The sooner the better.

You should also get perception and luck to unlock the Better Criticals perk.
Endurance never hurts, nor does Agility.
Then get the Sub-dermal implant.

After that, take your pick.

I find perception and charisma very useful in dialogues