I went with Cyber Tech , Scavenging and Underworld trading for my slinger during the Thanksgiving beta and was happy with the results I got with what little time I had to mess around with it.
Here's a few reason why:
First : The first few companions we get have bonuses that help out.
Corso + 5 Under World Trading and + 5 Arms Tech Crit
Bowdar +10 Cyber Tech +10 Scavenging
How big a difference those make I'm not sure, but I'm sure it helps some
Second: Unique items that we are able to make, some one all ready mentioned star ship mods, also speeder bikes and further down the tree reusable grenades that add more dps and cc utility.
Third : Ear pieces that can give us some nice extra bumps to our stats.
Lastly during the beta I had no real issues gather the materials I needed to make just about anything I wanted to make when I wanted to make it, unless I was missing a schematic for it. Fortunetly I did figure out that we can buy more schematics from the trainer once we reach a certain lvl of Cyber tech. Just my 2 cents