Don't limit yourself to just one side of the class. You want to be flexible, and able to fill your teams weak points, no matter where they may be. Personally, this is how it goes for my group:
We have 2 Hunters, 2 Warlocks, and 2 Titans. Both Warlocks are Sunsingers, for the self-revive ability. This is because they're not the absolute strongest of players, and the ability makes them able to be flexible. Dying doesn't mean instant doom. It also let's them be medics, in that they can run into an incredibly shitty situation to revive someone, and if they die it isn't a concern. The titans are both Strikers, but this is because the slam helps them get out of bad situations throughout the raid, and there really isn't a fight where the shield is a better "oh shit" button. Our hunters (me being one of them) change spec based on the fight.
For the gate, we go Bladedancer so that we can quickly move to other sections, clear out minotaurs/goblins/whatever, but Gunslinger is just as viable here. Do what you want. For the Templar, I think Bladedancer is best during the opening sections of the fight. Once you get to the actual boss battle, I suggest Gunslinger because ideally your relic holder should be killing all the harpies, and if they miss a couple they aren't hard to kill, so you really never should need to Bladedance your way to freedom. Gunslinger's super is great for clearing extra harpies across the room, killing oracles, and hitting the boss as well.
For the maze, go Bladedancer. Invisibility is awesome here. For Atheon, see the above.
Lemme know if you have any questions, although I'm not the most versed player, I've cleared the raid twice on Normal, almost cleared it the first week it was out (got to Atheon) and plan on starting Hard mode in a week or two once our lower level players hit level 28. I've also got WoW progression experience if that means anything.