Both are available relatively early and carry to endgame. Bloodhound's Fang is a curved greatsword with a dodge-attack; Nagakiba is the longest katana with incredible reach. Two very different weapons for different playstyles.
Bloodhound's Fang
Beginners and safe gameplay
Strengths
- Bloodhound's Finesse has built-in dodge
- Available from first evergaol in Limgrave
- Somber upgrade path (cheaper to upgrade)
- Built-in bleed without affinity investment
- Teaches good combat fundamentals
Weaknesses
- Cannot change Ash of War
- Somber upgrade limits customization
- Curved greatsword moveset is niche
- Requires both Str and Dex
VS
Nagakiba
Range advantage and aggressive play
Strengths
- Longest katana reach in the game
- Accepts Ashes of War and infusions
- Running R2 poke outranges everything
- Blood affinity for devastating bleed
- More customizable than unique weapons
Weaknesses
- Requires Yura's questline to obtain
- Regular upgrade path needs more stones
- Less forgiving without dodge-attack skill
- Needs Arcane for optimal blood build
Verdict
Bloodhound's Fang is the better first-timer weapon — it teaches you how to play and carries to endgame safely. Nagakiba is the better veteran weapon — its range and customization reward players who understand the game's systems.