I bought some beard balm to try after seeing people mention it in this Thread, waste of time. I'll stick with beard oils, far easier to apply and I can actually see a difference in my beard using it unlike the balm.
I think balms and oils are relative to the person using them, they both moisturise the hair and make it softer, but they have different uses.
If I remember correctly, Balms will provide more hold to your beard to keep it in style easier, if you have a particularly thin beard, it will also help to give it a thicker appearance.
Oils will cleanse the skin beneath the beard, moisturising it to prevent itching if you're prone to dry skin. It's also easier to work in than a balm, so it's a lot less effort.
Since I am prone to dry skin I stick with the oil, as it keeps my face moisturised and I don't get an itchy face.