My advice: It depends on how you'll be using the prop.
It it's just for display, on the wall on in a collection, then you'll want it sized 'true to life' so that you (as a human) are picking up something sized for a Dwarf. So the 39" option
If you're planing on a Thorin costume where you'll be dressed as a Dwarf, then you'll want the 49" option. That way you and the sword will look in proportion.
My $0.02 - hope it helps