The Calibur/Leviathan line is the vanilla sword that will serve you well through the entire game. It's easy to get all the recipes and since it only does normal damage, you'll never see damage variation. Its charge attack is arguably the best in the game as well; once you learn how to use it you can clear a lot of space very quickly.

The Nightblade does shadow damage as well, so any fiends/undead you run into you'll have to switch weapons. On the other hand, you'll do extra damage to slime/gremlins. Damage-wise compared to the Leviathan, it's the same against beast/constructs, but the charge is a bit less useful.

The Divine Avenger is the choice of a lot of players in T3 for a couple reasons: you typically can't unleash an attack chain without getting hit so you just want a large first hit, and its charge attack is ranged with a large knockback.

Personally I think the best sword for a new player is the Calibur/Leviathan line just because all the recipes are in town and it's not situational.