Someone (forgot who) mentioned earlier about the effects of sea and land strike. I thought I read somewhere that a sea strike is supposed to be much more destructive than a land strike.
The reason being the tsunamis created would cause damage to many coastal cities surrounding that ocean, and all the most heavily populated cities in the world are coastal cities.
So instead of digging a big hole in the ground, the energy released by the blast would be carried by water to reach a wider area.
Of course, all these is talking about the biggies. A basketball type would be better off dropping into the Pacific.