some more AD&D class rambling...
On a logical level thieves, assassins and monks make more sense to me as sub-classes of fighter -
paladins and rangers as subclasses of cleric and druid respectively. But I don't like the division of magic into divine/arcane, so I think that the cleric & magic user should be merged into one class, with a few permutation subclasses:
Magic User (learns magic user & cleric spells)
- Illusionist (learns magic user & illusionist spells)
- Druid (learns magic user & druid spells)
and heretical though it is (they can cast spells after all...)
This is, mind you, just logical ordering