GS or TFP?

TFP is more relevant across modes right now. He is very useful in P3 of AAT Raid, can be used in top empire teams, is needed for a mod challenge (potency which definitely has use for some toons), and their ships are about equally useful (solid ships). GS was the first character i farmed from cantina and I loved him for a while, but TFP is better right now and has more utility.

Tie Fighter Pilot has both utility and big damage, plus an AOE.

It really depends on where you are at (what your shard is) but eventually you will need TFP over GS,

GS i so 2016

If you start, GS is easier to put on every team. But if you plan to run an Empire team, or a debuff team, use TFP.
GS is also the easiest toon to gear up.