She had only died twice, but I think the first one ( when she sealed Inuyasha to the baum ) was Mehr tragic because she died in misery, heartache, and betrayal.
But in her Sekunde death, she died happy that Inuyasha will be ok, so her soul could rest in peace.
It was a sad Tag for everyone, but remember: kikyo sagte her soul is at peace and is saved.
She also wanted Kagome to take care of Inuyasha because she wanted him to be happy.
That is why I think her first death was the most tragic.