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 $\left(4n + 2\right)\pi$ electrons ($n = 0$ or any positive integer)

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