My (incredibly biased) vote is for /EM, having played one for ages. Admittedly, I made my archer ~10 years ago before /TA was an option for blasters, and while it is a cool and thematic pairing if you want more utility arrows and hate meleeing, it's far from the only one.
/TA, between Eagle Eye, Agility, and Gymnastics, offers +20% accuracy, +20% recharge, +50% recovery, +225% regen, +1.75% def, KD/Immob protection, and some speed boosts and mes resistance (still hits you, but wears off quicker). That's sweet, not gonna lie.
Energy Manipulation offers a variety of high-damage smashing/energy melee attacks, which are very useful versus ghosts, robots, and other highly-lethal-resistant foes. If CoT ghosts have 40+% lethal resistance, an A/TA blaster is going to have a bad time (their immobilize only does ~20% more damage than Snap Shot, as an 8 second DoT), but an A/EM blaster can pop off Bone Smasher + Total Focus to annihilate it. It also gives a blaster Energize; that's not really a selling point with every secondary offering some sort of sustain tools these days, but it IS among the nicer options for that now instead of the trash it was many issues ago, with permanent +120% global endurance reduction and the same +regen as Eagle Eye. Power Boost is fine, but being able to turn Aid Self / Aid Other into a full heal is admittedly rather niche. None of that is all that important though.
Boost Range is the real selling point here. Perma right out of the box with SOs, this power is the equivalent of 3-slotting all your abilities with range SOs, an effect that no one ever does because you need to slot them for acc/dam/rech instead, but is surprisingly nice once you try out. As an Archer, your bread and butter is mowing down basically every spawn with a brutal volley of Rain of Arrows/Fistful of Arrows/Explosive Arrow, but with Boost Range, you can do that full chain from over 100' away, and joust around to mow down any lucky bosses that survived the initial salvo. Being able to tag the ENTIRE battle with Fistful no matter how spread out they are is a huge QoL perk, and this makes kiting a breeze if you want to cheese fights with hover / joust around with Combat Jumping + Hurdle. As an archer, being able to just tag enemies no matter how far they are feels RIGHT. It also affects non-attack powers; an /EM Blaster with Teleport is THE fastest character in the game if you need to cross long distances (Shadow Shard maps, I'm looking at you).
