Is it better to break the fast at home or in the mosque?

If what the
questioner is referring to is food that is eaten to distinguish between the
time of fasting and the time when it is permissible to eat, such as eating
dates and drinking water and so on, then it is mustahabb to hasten to do
that, because the Prophet (peace and blessings of Allaah be upon him)
said: “The people will continue to be fine so long as they hasten to break
the fast.” Narrated by al-Bukhaari, 1957; Muslim, 1098. See also question
no. 13999. 

But if what
is meant is what people eat after praying (the iftar meal), then there is
nothing narrated concerning that in the Sunnah as far as I know, but each
person must weigh up different factors. Eating iftar in the mosque with the
congregation serves the interest of bringing Muslims together and helping
them get to know one another and become friends, reviving the spirit of
cooperation and so on. 

Eating iftar
with the family at home serves the interest of bringing the family together,
discussing family matters, reinforcing the bonds between family members,
teaching children the etiquette of eating and conversing, and so on; it
increases the love between husband and wife, and between parents and
children, and so on. 

What the
head of the household must do is strike a balance between these interests.
He could choose some days to eat iftar with his family and some days to eat
iftar with the congregation in the mosque, whilst noting that his duty to
take care of his family and children, teaching them the etiquette and
teachings of Islam takes precedence over the naafil action of meeting with
friends in the mosque, because he can meet them at Taraweeh prayers or in a
general gathering and so on.

And Allaah
knows best.