each unique item has a specific requirement. Such as "straight sword" +10, or great sword, etc. it doesn't matter what version of a straight sword use.
The only special thing I guess would be sif making two different great swords.
If you make a great sword +10 it will turn into a cursed sword able to hit ghosts without use of transient curse (but you still can't block ghosts without it and you take more damage without it, so thats iffy.) If you make a broken straight sword +10 it will turn into a holy great sword.
Alternatively it can be made into a shield via +10, pretty sure any shield works fine.
The stats are always the same for unique weapons though, regardless of you using a longsword vs a broadsword.