I would stick with EA:FA + Spitfire, simply cause you dont have to watch your turret placement. Further i think that Spitfire does a lot more damage in combo with the ballistics passive than Polar+Impale
I have been going back and forth on this. I found it easier to have EA-FA with the spitfire, but it seemed like things died faster with my current build. I just keep throwing my Polar Stations out in front of me and only using MS as the only self cast. Tonight I plan on trying this build without using ballistics and picking up steady aim. The Polar Station 3 spender build is kind of boring because you really don't do anything. I have a calamity I'm waiting on a RG to drop and give it a try as well.
I'd also stick with EA:FA, FA with sentries is simply amazing, and, if you are not considering ballistics+spitfire with MS build, EA:FA is going to net you more damage (with Ballistics+spitfire and MS build, both would be very close until you reach the 2.16 breakpoint)
Same situation. I have a Krinder too so i can use EA instead of waiting for sentries to do all the work and i'm undecided if using Polar Station or Frost Arrow to proc Cull the Weak.... As the poster above noted, i think i'll stick to Spitfire + Frost Arrow with Ballistic and see how things are going... at least i shouldn't play geometry when placing sentries
I played a little more and when I'm in tight spaces the Polar Stations are amazing. You can pretty much chain the mobs to keep the chilled affect all the time and no mobs even get close to you. Outside enviroments are a little tricky and the EA-FA seems like a better play. The time to kill mobs still seem a little better with Polar Station 3 spender with CA, MS, and Imp. Once you get two sentries down nothing lives more than a few seconds. I'm mainly playing t6.
I run Fire CA+MS+IA and Polar Station w/o Ballistic and i think it works very well. When i have the hatred and time for it i can fire off some IA. As for the placement of Polar Station(when using it as your only slow) i think it comes easy and naturally. If you jump the mob then you place it on the mob. If the mob jumps you, you place it on yourself. And in open areas you just keep them spread.