O que Sirius achou?
Na verdade não é nada claro que Sirius tenha pensado que era um local de encontro geralmente melhor; a citação referenciada é uma resposta a uma interjeição de Hermione, e Sirius está comentando sobre a falha de uma linha específica de raciocínio:
"You want to choose your meeting places more carefully," said Sirius, grinning still more broadly. "The Hog's Head, I ask you."
"Well,it was better than the Three Broomsticks!" said Hermione defensively. "That's always packed with people -"
"Which means you’d have been harder to overhear," said Sirius. "You've got a lot to learn, Hermione."
Order of the Phoenix Chapter 17: "Educational Decree Number Twenty-Four"
Mas mesmo se assumirmos que o Sirius faz pensar que o Three Broomsticks é um local melhor, vale a pena notar que ele só acredita nisso em comparação ao Hog's Head. E, para ser justo, esta não é uma opinião irracional.
As Três Vassouras vs. A Cabeça do Javali
A questão alega que um grande grupo de crianças reunidas em uma taverna seria suspeito, mas o Três Vassouras não é estranho para os alunos de Hogwarts; como aprendemos em Cálice de Fogo :
The Three Broomsticks was packed, mainly with Hogwarts students enjoying their free afternoon, but also with a variety of magical people Harry rarely saw anywhere else.
Goblet of Fire Chapter 19: "The Hungarian Horntail"
O Hog's Head, por outro lado, é um mergulho , praticamente vazio e não costuma ser visitado pelos alunos:
Embora uma grande reunião de jovens em qualquer local possa ser motivo de suspeita, certamente parece menos suspeito que eles se encontrem em um hangout de estudantes conhecido, em vez de um bar sujo e de passagem, freqüentado por pessoas como Mundungus Fletcher.I've told the others to meet us in the Hog's Head, that other pub, you know the one, it's not on the main road. I think it's a bit... you know... dodgy... but students don't normally go in there, so I don't think we'll be overheard."
[...]
It was not at all like the Three Broomsticks, whose large bar gave an impression of gleaming warmth and cleanliness. The Hog’s Head bar comprised one small, dingy and very dirty room that smelled strongly of something that might have been goats. The bay windows were so encrusted with grime that very little daylight could permeate the room, which was lit instead with the stubs of candles sitting on rough wooden tables. The floor seemed at first glance to be compressed earth, though as Harry stepped on to it he realized that there was stone beneath what seemed to be the accumulated filth of centuries.
[...]
There was a man at the bar whose whole head was wrapped in dirty grey bandages, though he was still managing to gulp endless glasses of some smoking, fiery substance through a slit over his mouth; two figures shrouded in hoods sat at a table in one of the windows; Harry might have thought them Dementors if they had not been talking in strong Yorkshire accents, and in a shadowy corner beside the fireplace sat a witch with a thick, black veil that fell to her toes. They could just see the tip of her nose because it caused the veil to protrude slightly.
Order of the Phoenix Chapter 16: "In the Hog's Head"