Well the onyx blade is a 1h sword, so it'll have less range and a lower dmg formula than a 2h sword. Also, I'm pretty sure it is fast (5), while the lionheart as well as the jap map is fast (4). Lionheart is also 55 atk base clean, not 45, and it's also 10 levels lower so you can use it earlier. A 100% lionheart will do more damage over time than a 100% onyx blade, as well as coming pretty close in damage per hit.
You should definitely get the lionheart, then switch over to the japanese map if you can at lv 50. Those 2 swords are the best options available and pretty much pwn everything else.
You should definitely get the lionheart, then switch over to the japanese map if you can at lv 50. Those 2 swords are the best options available and pretty much pwn everything else.