AA would be the most comfortable option as they fly nice 737-800s with more room in coach
Flying WN from LAX?

The lineups at their gates in T1 are always insane! Give yourself enough time to walk over to T1 and clear security, etc. Keep in mind UA also flies LAX-SMF (mainline and RJ) and they usually match the WN sale fares.
Another option is to fly AS or WN from LAX to RNO for a gambling side trip and then drive to Sacramento. It's a scenic 2 hour drive through mountains.