Just wanted to chime in on how great the Alaska deals are from SEA to Long Beach. I just booked a few days ago at the $99 each way fare for our late October trip and started a thread on this too so you may want to look for that. It may have been last week.
Anyway, you can probably get a cheaper price through Southwest when they have a sale or through Ding! if you're willing to have a layover in N. Cal but after doing that once with kids we decided it was worth the extra $10-20 each way to have a non-stop flight. I also looked at Jet Blue and the prices were the same as Alaska currently but they only had one flight choice for our departure date and 2 on our return date, and these were very early morning or evening flights. Alaska had 4 flights per day to choose from and the times fit us better.
Also, I found out that if flight prices go down on Alaska after you've booked you can call and they will credit you for a future flight the price difference.
As far as airports go, we've flown into Long Beach and Ontario. Ontario is a bit further and you have to take a shuttle to the rental cars. It's not a bad choice though if you get a great deal. We do much prefer Long Beach. It's very small, fast security, rental cars are right there. Love it!!