Some vault titles differ from region to region. For example, 101 Dalmatians was already released in some regions, but is still in the vault until next year in the US. So if we exclude those titles currently vaulted, as well as those that have been previously released as a steel of some kind, that leaves us with these possibilities:
Dumbo
Alice in Wonderland
Peter Pan (will be returning to the vault around this time next year)
101 Dalmatians (to be released from the vault in 2014, but already released in UK)
Sword in the Stone
Jungle Book (to be released from the vault in 2014)
The Aristocats
Robin Hood
Many Adventures of Winnie the Pooh
The Rescuers
The Fox and the Hound
The Black Cauldron
The Great Mouse Detective
Oliver & Company
The Little Mermaid (to be released from the vault this year)
The Rescuers Down Under
Pocahontas
The Hunchback of Notre Dame
Hercules
Mulan
Tarzan
Dinosaur
The Emperor's New Groove
Atlantis
Lilo & Stitch
Treasure Planet
Brother Bear
Home on the Range
Bolt
Tangled
Based on this list, I think the priority should be Peter Pan, as it is the only title already available that will be returning to the vault.
If we separate this list further into those titles already released on blu-ray vs. not yet released, we have:
Released in the UK and/or US: (in my opinion, these titles should get priority, since they already missed the opportunity for the steel treatment when they were initially released)
Dumbo
Alice in Wonderland
Peter Pan
101 Dalmatians
The Aristocats
The Rescuers
The Fox and the Hound
The Great Mouse Detective
The Rescuers Down Under
Pocahontas
Hunchback of Notre Dame
Mulan
Tarzan
Dinosaur
Treasure Planet
Brother Bear
Home on the Range
Bolt
Tangled
Not yet released in the UK and/or US:
Sword in the Stone
Jungle Book
Robin Hood
Many Adventure of Winnie the Pooh
The Black Cauldron
Oliver & Company
Hercules
The Emperor's New Groove
Atlantis
Lilo & Stitch