Assuming one has done the Thieves' Guild quests to completion and the main quest, if the Last Dragonborn became a vampire, who would actually have their soul when forever ends up being all too short? As a Nightingale would it be Nocturnal? As a vampire, would it be Spicy Meat Bol? As a hero and Dragonborn, would it be Akatosh or Shor? Or could it even be the All-Maker, and the Skaal have the truth of it all because they're awesome?

Would be great if it was the Skaal. Something about a reclusive tribe of monotheists existing in a world where everyone else takes the power of multiple 'divines' for granted is really appealing.

I like to believe that the dragonborn can choose where to go, cause while most people dedicate themselves to a certain divine/daedric prince, the dragonborn can become the champion of every daedric prince and go to sovngarde anyways.

A dragon soul is a subgradient fragment of the soul of Akatosh. So all the "Who gets the soul" is moot... it's Akatosh's. The joke's on all those Princes.

They all would play poker; the winner takes the soul.

So the Last Dragonborn can play the tease with every soul snaring deity floating out there and get away scot free when they come a-knockin'?

Sounds like it... except that his/her soul belongs to Akatosh. I do wonder what that means, though. There's not really an 'afterlife' associated with Akatosh or any of the Divines, is there?

Atherius.