Which of the following molecule/species is most stable?

Four Criteria for Aromaticity

• The molecule is cyclic (a ring of atoms)
• The molecule is planar (all atoms in the molecule lie in the same plane)
• The molecule is fully conjugated (p orbitals at every atom in the ring)
• The molecule has $\left(4\mathrm{n}+2\right) \mathrm{\pi }$ electrons ($\mathrm{n}=0$ or any positive integer)

Others do not follow these rules, hence the answer is option A.