I usually go with :
Pathfinder : because it makes tactical moves easier. Not having to waste turns climbing is unvaluable and so is wrongfooting the enemy in a swamp.
Gifted : because a +4 to melee defense, at low level, is great and does a lot to improve survival rates.
Colossus : again, survival is much more important at low level than sheer performance.
That’s the three basics for any new guy, so he can keep up with the rest of the company.
From there, it depends.
Shield Expert :
My main battleline is shields and spears, backed by polearms on second line, with the captain (and sole surviving of the three founder) using a sword and shield to roll the enemy’s flank.
Once the battle really start (or against orcs), they switch to axes and shields.
Having good shields made the difference between life and death more than once.
If the new guy is meant to integrate the main battleline (and most are, since most casualties come from there), he goes shield expert.
Axe Mastery :
The go-to for the main battleline. You split shields faster and therefor kill enemies faster, which means less injuries to your dudes. Also, less fatigue allows for more agressive play.
Sword Mastery :
Only my captain has it. And that’s because he is the only one with a sword.
Sergeant :
Mainly a RP thing but I take it for the three polearm dudes, as they can easily move along the line.
Battle Forged :
Increased armor is always good.