Agility-based swords (shortsword, sabre, hunting sword) differ from longswords in that they’re agility-based (a minimum level of agility is required for them to deal nominal damage, higher agility increases this damage further) and they use different combos.
There are several differences between shortsword, sabre and hunting swords. Sabres are generally balanced towards cutting vs stabbing as are some hunting swords. Shortswords have better defence stats than other one handed swords. Some hunting swords have very good durability stat, but defense is generally not the best. If you want to use a one handed sword without a shield, go for the shortsword. Shortswords also appear to have the highest quality among other one handed swords.
In comparison to longswords, one handed swords can do most (but not all!) combos with a shield equipped, while longswords can still be used with a shield equipped, but can perform no combos. On the other hand longswords have the highest defense stat of all weapons, which makes them the best weapon to use with a torch equipped.
Swords in general have a significantly higher speed and reach compared to maces and axes, but fare badly against plate armor (save for the best swords).
If you want to play it safe, you will need at least one longsword, one short weapon, one shield and a torch at all times so you can succesfully engage archers and enemies in the dark.
When playing a melee-oriented character, one handed swords have no specific advantage, as you will need strength for carrying heavy armor and using anti-armor weaponry, while you will also level up agility while using strength-based weapons.