Mage/Cleric, Dual, Multi-Class, Advice?

So I wanted to make a mage who can cast high level priest spells, contingency -> heal and so forth.

I realize that there are 3 options:

Mage/Cleric Multi

Mage dual'ed to Cleric (Possibly a specialist mage school)

Cleric dual'ed to Mage (Possibly Priest of Lathander)

Can anyone explain to me what are the benefits/cons of these? Ideally, I would like my caster to be able to cast at least FOUR level 9 mage spells, if not more.

I heard something about the number of memorization can go down using a multi..is it true?