In Mafia Wars, not including reward points weapons, the TNT is the best weapon for attacking, and the Gaff Hook is the best weapon for defending. TNT is dropped from the "Raid the Arms Depot" job and the Gaff Hook is dropped from the "Pillage a Shipyard" job. If you are going by combined stats, TNT has the highest at 62.
TNT (+62) Cuban Weapon found in the job 'Raid The Arms Depot'
Armored State Car (+68) Cuban Vehicle found in the job 'Storm The Presidential Palacet'
Guerrilla Squad (+64) Cuban Armor found in the job 'Supply The FRG With Some Extra Muscle'