4-Aminopyridine (pKaH 9.2) is a much stronger base than pyridine (5.2). In it, protonation occurs at the ring nitrogen because

1. Athe amino nitrogen lone pair is part of the aromatic sextet so only the ring nitrogen can be protonated
2. Bprotonation of the amino group is impossible because it is sp${}^3$ hybridised
3. Cthe amino group withdraws electron density from the ring by $-M$ effect
4. Dthe resulting cation is stabilised by a resonance structure in which the amino nitrogen donates its lone pair to carry the positive charge