Paladin has cheaper access to Holy spells (including healing, HoBS, etc) and Arcane spells (e.g. Dispel, Teleport). He's also the only Mage fully trained in [mwcard=MWSTX1CKE01]Armor Ward[/mwcard]. For this reason, he's also more likely to have room for out-of-school spells like Dancing Scimitar - although in principle either could use it. He can also have Cassiel cast most of his healing and protection spells for him, allowing him to focus on the offensive, plus get a Guard/Intercept to boot (via his "Radiant Breastplate" chestpiece and "Dawn's Valor" shield).
Paladin's Cloak, Shield, Helm, Breastplate and Sword can't be used by Warlord. There aren't really any Warlord Only equipment or other spells that a "tank" really needs.
Warlord is more likely to choose a Level 3-4 War or Earth buddy that a Paladin would pay double sbp's for (e.g. Dwarves, Golems, Earth Elemental), while a Paladin has the new Holy & War soldiers along with all the Holy options in school (e.g. Knights, Angels, Clerics, Unicorns).
That's about it.
Oh, and Smite is a great finisher.