Why did Gandalf choose Bilbo?

[Inziladun]

Originally Posted by lindil

But Gandalf, being 'a steward of all things' saw the need of the hobbits in general even as he saw the potential of Bilbo in particular.

To that and what's been said above, add the observation by Gandalf that Bilbo was "meant" to find the Ring. There clearly seems to be an element of destiny in Gandalf's choice, whether or not he himself was conscious of it.