How potent is Antimatter compared to Uranium or Plutonium?

Typical fission efficiencies in an efficient fission bomb is on the order of 50% (the fissile material obviously becomes more diluted as it splits into fission products, so 100% fission is unachievable). read more

Extremely. The fission of a uranium-235 atom generates about 202.5 MeV of energy from a U-235 atom and a neutron (total mass = 236.05 a.m.u.). read more

Plutonium has favorable nuclear characteristics as compared with Uranium (namely: it has a broader neutron cross section - if that means anything to you (I will explain in a bit) - and it releases a slightly larger amount of energy per fission event. read more