BAB or HD to initiative

[molten_dragon]

BAB to Init or HD to Init

My suggestion would be neither. Just create a new Initiative progression for each class that's either full, 3/4, or 1/2 HD just like BAB. And then you can give each class whatever initiative bonus makes sense. So for the core classes you might go with:

Full Initiative Bonus
Monk
Ranger
Rogue

3/4 Initiative Bonus
Barbarian
Bard
Fighter
Paladin

1/2 Initiative Bonus
Cleric
Druid
Sorcerer
Wizard