The best one-handed "sword and shield" sword is probably the Balder Side Sword, followed by the Sunlight Straight Sword, but the Longsword isn't bad, really. The falchion is very decent, as is the shotel: they're fast and scale with dex and shotels can bypass shields. For a stronger but slightly slower sword, the claymore is very very good too.
I prefer the Longsword (or Broadsword for that matter) to the Balder Swag, personally. Mainly because I think the forward stepping R2 on the Longsword beats the repeating stab of Balder Swag, especially in PvP situations where you need to follow up on a miss or break guards. I only do base-SL runs anymore though so I'm not speaking from the perspective on the efficacy of a "build".