A lot of it comes down to how you play. I imagine a PvP'er will get more utility out of Bio than Armor, but as a solo quester I come down on the Armormech side of the argument. Since all of Havoc Squad (minus Fourex) wear exactly the same thing, gearing your team becomes cake. Then you get to gear up the companions of your alts (that's a total of 2 toons and 14 companions for hvy and med armor). Want money? Consider that your crafted gear is going to be better than any looted or rewarded green, and most blues if you're over-leveling the quests. Greens get sold to vendors, blues go to the GTN. I spent most of the game actively hunting for elites with my Commando, something I never would've done with my far-squisher Sniper. To me, armormech has far more long-term functionality for the solo player.

I've got a Sniper up to 22 and I would say that the class is less forgiving of tactical errors than many others. You can overcome this by over-leveling quests or with gear, but if you think you can just faceroll through a lvl 17 quest at 15, you're going to get smoked.