Which is a better early game choice for a Stealth/Nonlethal character, Agility or Possession?
My first time through Dishonored, I'm playing the way I played Deus Ex - silent and compassionate. I've got a couple runes and I've just met Granny Rags, so I'm not very far into the game at all. I'm trying to figure out where best to allocate my points to enable a sneaky playstyle.
Things like Shadow Kill and Bloodthirsty are useless to me, because if I'm playing properly, I should never be killing anyone. I know that in most Deus Ex-likes, there's a heavily-guarded path that requires nothing but murder to get through, and a lightly-guarded path that requires certain abilities to get through. This is the path I plan to take through the game.
Reading the descriptions of the various powers, it seems that Agility would be helpful for the greater jump height, but Possession would be helpful to crawl through small spaces as a rat...but I don't know how many small places there will be versus how many high places. Also, Possession II would allow me to walk enemies into lonely areas so that I could dispatch them more easily...but I don't know if I'm going to have enough runes and mana to make that strategy viable anytime soon.
In the early game, which is more useful to a stealth-based character, the extra jump height granted by Agility or the ability to travel through small spaces and relocate enemies granted by Possession?
First of all, if you pick up all the runes, you should be able to grab Blink II, Agility I and Possession I by the end of the first mission. All three are enormously useful, however, within that first mission, I'd have to say the most valuable pickup is Blink II. You didn't mention it, but it really is the single most valuable skill I've found for stealth runs. After that, choosing between Agility and Possession is mostly a matter of taste. I'd favor Agility personally, but that has more to do with my fondness for blink spam and distaste for using Mana on anything else than it does to do with any difference in the usefulness of the two skills, and you can easily grab Possession II quite early on in the second mission, where I did find it pretty useful.