If you know you're flying coach and won't fly enough for status/upgrades, everything about southwest is better than the legacy carriers. Choosing your seat is a blessing*.
Names things that are better. I'm having a hard time thinking of any. Also I don't understand the choosing seat is a blessing thing.
best flight change policy
Entertainment(free)/wifi on every flight and it always works (at last I've had better luck than United)
Best domestic flight options (unless you're going to Wyoming or something)
no rj's
if you see a fat smelly person in a seat, you can walk past them and find another (again, this assumes you aren't a dumbass)
no baggage fees
free snacks
again, their biggest knock is status and upgrades. Getting a10 or better is a pretty worthless perk