Thanks everyone who contributed to the thread so far. It's been extremely helpful, especially @Sunsette's write-ups on Energy Blast, Beam Rifle, and Energy Armor. As well as @Hopeling's Electric Armor write-up.
I'm eagerly awaiting write-ups on Electric Blast and Radiation Blast. As well as Radiation Armor.
Elec/, Rad/, Energy/, BR/ along with /Elec, /Energy, and /Rad are all powersets I'm looking at to bring my power-armored alien Sentinel to life. I've been extremely indecisive as of late and rerolled my character half-a-dozen times. All feel "okay" but it's hard to know which sets come into their own at later levels before the indecisiveness takes hold. I'm concerned about how important it is across most Sentinel sets to "softcap" defenses for a variety of damage types, and most armors I'm interested in have none outside of Energy (that being Electric, Radiation, and Fiery Aura). There's a lot I'm learning and I recently did a crash course on how Enhancements work because when I first played CoH it was all just sort of gibberish to me.
I like the idea of focusing primarily on primary ranged power-sets with a couple of thematically appropriate epic powers to add a bit of variety in attacks or control. That's one thing great about most of these Sentinel secondaries is that they primarily consist of toggles and passives with the occasional click ability that you may or may not have to use. I generally use Fly/Hover and I don't really like the idea of dipping into Leaping or Fighting just for a couple more toggles but I'll do it to shore up defenses and you can usually just toggle and forget they exist if your Endurance can support it.
As for each of the primary powers I'm interested in, Radiation seems to focus more on DoT and it feels fairly ineffectual when in large groups while leveling up, but it looks really good aesthetically. Electric Blast wouldn't be my first choice in a thematic power-set but it still fits the powered-armor feel and it does really good damage. I'm intrigued to actually make a "Sapper" build along with Electric Armor that can actually keep enemies drained (though I seen in the Electric Armor write-up that Endurance-drain is a disappointing form of control at endgame). Energy fits the theme perfectly but after watching @Sunsette's frustration with Energy's low damage output in addition to the crazy KB (as fun as it is, you'll run into trouble in teams unless you position yourself perfectly, which is something I'd be willing to do if Energy's damage was higher).
I guess what I'm getting at is I'm trying to think what combination of Electric Blast, Radiation Blast, Energy Blast, Electric Armor, Radiation Armor, and Energy Aura tends to give you a well-rounded, effective Sentinel at endgame.