Either way you are selling your soul to a Daedric Lord, though at least as a Listener you do it out of your own will rather than be cheated to it by your so-called "partner".
As a Nightingale your bound to Nocturnal even in the afterlife.
However as a Listener, you kill a great many innocent people.
Tough choice. Live a thieves life or a killer's life. From an afterlife standpoint I'd have to go with the Listener.
I thought Listener also becomes bound to afterlife service. Isn't that what that Lucien guy is doing now?
Well as listener...in the afterlife you would serve Sithis in the way that Lucien does...so either way your forever bound to a non-corporeal existence.
Why not both?
I'm thinking of making my character abandon his duties as the TG guildmaster, and running off to join the DB, thereby betraying his contract with nocturnal and being forever cursed in the eyes of gods and men.... quite a fitting way to end a character lol