Both episodes give limelight time to heroes other than Kirk, even if McCoy spends most of his rotting in a jail. The exposure gives a bit of character development to the sidekicks involved, but IMHO McCoy gets the better half of the bargain even if all of his material is on his past rather than his present.
Both episodes feature a spatial light show of some interest, as well as a starfaring alien culture that actually possesses quite a bit of history, structure and spatial scope. This is more or less the first time we see aliens having colonies of their own, or being at odds with the Federation yet not totally stamped on like Romulans or Klingons - or operating starships of their own that have rather specific functions rather than being generic threat vessels. Points for that bit of worldbuilding.
Also, both shows feature a combination of action and brainwork in the solving of the problem of the week, with the brainwork carrying the day without detracting from the space action or the whine of the phasers. There's a degree of anticlimax to the resolutions in both, too: a bit of medicobabble in which McCoy admits to having originally fumbled exonerates him from the hatred of those whose loved ones the fumbling killed, while complete inaction on the part of Spock, Sulu and Uhura allows them to live through the climax where two aliens, one machine, the other feline, slug it out in a highly uneven battle of wits.
Ultimately, I find this a surprisingly difficult choice. "Albatross" has the more touching concept and the more naturally flowing dialogue, while "Slaver Weapon" has more twists and turns and novel conceptlets. But the guest stars of "Slaver Weapon" appear an undistinguished mass of generic villains, while those of "Albatross" are sympathetic even when antagonist. The quality of the opposition tilts my balance towards "Albatross", with a bit of extra weight from the fact that most of the action in "Slaver Weapon", realistically but annoyingly, leads nowhere. It's a close call nevertheless.