American Airlines Points versus Southwest Rapid Rewards, which rewards better for domestic US flights?

the AA million mile thing has got my head thinking that perhaps I should be using AA's instead of Southwest

Each year I take about 8 Roundtrips via southwest (all within CA, im a colleget student) for each roundtrip i get 4.0 RR credits (2.0 for each one-way trip), so, after 4 RT's i get a Rapid Reward

under the same scenario, could I receive better benefits (ie. more miles for free flight in less time) if I fly with American Airlines? [AA does fly the same route I take]