Just to play devil's advocate:
Hell and Wraith swords have another advantage over blood thorns: cost. Blood Thorns cost twice as much as Hell swords, they do less damage, and they have no special abilities to speak of (unless your SC has blood magic, then of course they're the best choice).
Hell Swords make you go berzerk, and give +3 attack and fire resistance. Wraith Swords give +3 defense, I believe, which is nice, although admittedly not as much as you could get from a shield. Although a decent shield at 10 gems puts the total cost at a whopping 30 gems and/or slaves for the blood thorn/shield combo, whereas it's only 10 gems for the Hell/Wraith sword.
So, I think in terms of cost
efit, the Hell Sword probably is the best bet. In terms of pure benefit, I agree the Blood thorn/shield combo is better.