When should the word granja be used instead of the word hacienda?
For exmaple, should one be used over the other when saying; 1) horse farm, 2) my farm, or 3) the Smith farm? Thanks.
5 Answers
Having my exposure to Spanish mainly in Mexico, and listening to conversations within my wife's family, I would probably consider the following:
hacienda would be more of a country estate with a grand house, possibly a chapel, other living quaters, gardens, etc. usually enclosed with walls for protection and privacy.
granja would be a farm but mainly for producing crops, milk or small animals (pigs, chickens, goats etc )
rancho would be a type of granja (farm) but more intended to raise anmials and stock (horses, cattle, etc). In American English...a horse ranch or cattle ranch.
So in response to your post... it would depend on what you or the Smith family do on your farms. The only example that gives me a clue would be "horse farm" that I would call "un rancho".
Hacienda is like a farm but so much bigger and granja is more rural. On an hacienda you can have for example thousand head of cattle (I don't know if I wrote well in spanish is "cabezas de ganado"), but in a granja you have a few of animals like. If you saw babe the gallant pig, that is the perfect example of granja.
=)
Qué interesante. Vivo en una granja. 
There's a lot of regional differences as MexGuy shows when he defines a classic Mexican (or Spanish) "hacienda" while, on the other hand, an Argentine "hacienda" is a big property like MexGuy's "rancho".
Taking some sort of average is difficult because of these differences but, assuming you're aiming at Mexican Spanish, follow MexGuy and say
"un rancho" (con caballos) "mi granja" if it grows produce and or livestock other than horses "la granja de los Smith" with a similar proviso. (or "de la familia Smith")
And this one even throws Estancia into the mix:
