Note wise, Parallel Universe is the easiest, but you need to be able to play fast with a pick or your fingers.
I could Have Lied. Add your own fun to that one.
The Zephyr Song is relatively easy all around, it's just a pain to remember the chorus order and you can easily trip over yourself.
Venice Queen too, actually I would start at the entire By The Way album for finger style.
Rain Dance Maggie is easy too.
Pea is easy (troll option).
For slap, easiest is IMO Green Heaven is simple, first slap song I learned, followed by Knock Me Down (if you play it simply it can sound good without embellishments).
