Yes, the little ones tend to be the most aggressive, with dachshunds at the top of the list, according to a new study in Applied Animal Behaviour Science. Chihuahua were next, followed by Jack Russells. Pitbulls are near the middle of the range. This is a classic quote:
Tony Fitt-Savage, president of the British Chihuahua Club, added: "I have had Chihuahuas for 30-odd years, and they've never put anybody into hospital. They can be a little bit stroppy."
Mr Fitt-Savage is, of course, a human oasis of calm. I couldn't find the original article so I have no data for beagles. Bassets are very sweet. My beagle-basset is sweetness personified; my pure-bred beagle has some mouthy attitude. My husband notes they each take after one of us.