A comparison of the relative stabilities computed at RB3LYP/6-311+G(d,p)//RB3LYP/6-31G(d)+ZPE of the neutral nido-single clusters and two vertex-sharing macropolyhedral nido:nido-clusters shows single-cluster nido-boranes with up to 11 vertexes to be energetically more favorable than isomeric macropolyhedral boranes. Extra hydrogen atoms at the open face have a significant influence on the relative stabilities of the single cluster nido-boranes vs nido:nido-macropolyhedral boranes. For anionic species, a clear-cut turning point for macropolyhedral preference is shifted to no less than 17 vertexes. Thermodynamically most stable neutral and anionic nido:nido-macropolyhedral boranes usually consist of a nido-10-vertex and a nido-11-vertex unit, respectively. The relative stabilities of isomeric neutral macropolyhedra reflect the patterns exhibited by the sum of thermodynamic stabilities of the individual clusters.