Fudo and Kaiten are boss as hell in Delve, if you have proper buffs. Kaiten when below 153tp, Fudo when above (153 assuming you're using Moonshade). Shoha if you're buffs/debuffs are bad. Namas if you iLVL a Yoichi too and get a crapton of buffs.
As for Amano vs Tsuru, it comes down to if you have Ionis, your hit builds, pulling hate and swapping to pdt, and human error.
Overall Amano is the better built weapon, but Ionis favors Tsuru. For the new BCNM and Mission Very Difficult fights, Amano will be best.