For Escorts, my favorite build is #2 above. 3 DHC, with a good borg-powered Quantum for the front, and #2 for rear (I like the har'gpeng, or whatever the hell the one with the purple radiation is, as Borg won't clear the damage, so you get a big secondary explosion). that lets you really get a good pounding from the front guns, can mix in torpedoes, rear turrets get involved, and then you can toss the big torpedo as you go by, or turn around.
For powers, really you want the high-yield cannon and scatter volley, and then same for torpedo powers (spread and high-yield). Having 2 Tac Teams is useful, as you can pump up your shots almost constantly, and then I've got Eng team to heal me, and a couple science debuffs/heals.
it's a little fragile, but can put out pretty devestating power. As long as you keep moving, and heal often, should be a good weapon. Just have to focus on one energy type, and commit to the escort instead of treating it like a cruiser.
I played cruisers all through the leveling process, and then found my groove with the escorts at endgame. Can't go back now, just way too slow/clunky for me. I like moving around rather than tanking and broadsiding, and favor the quick overpowering win to the slower method while absorbing damage.
Near as I can tell, SCI ships (and characters) are fairly useless in the game outside of having a decent BOFF on an away team, and really are a jack of all trades, master of none situation. PVE is really it at end game right now, and they can't tank or DPS, so kinda not worth having around. Not much they can add that the other two can't do, Cryptic missed the boat on making that class useful.