Tsukiyomi because you mentally fuck up your enemey and it's a near impossable Justu to escape and it's your own persnal world of witch you can do anything to the enemey to the point where there mind breaks

Chibaku Tensei because it was used by Pain and the great Rikudo Sennin to seal the juubi away so it is the strongest technique in the show

I indeed think Chibaku Tensei is the strongest jutsu in the show. My favourite goes out to Kirin or 64 Palm Jutsu though.

Reaper Death Seal is a deadly one as well.

Tsukiyomi because its your own world around you and you can hurt your enemy as long as you want and he will not escape (he cant escape) its an illusion but it hurts u alot in real life

RAIGA BOMB!!! 'nuff said...