Most folks that are going full freemium (not paying for donuts/cash) usually house farm. I'm keeping mine up until I own all the land. It allowed me to keep my head above water and able to afford all the new buildings when I leveled up. I started with a Brown house farm, upgraded to some Purple and removed my Browns, then went full Blue. I just recently removed all my Purple houses since I started visiting my town less often. It depends on your play style, how often you check your town, that should guide you to the house choice for your farm.
I went full geek and calculated the payouts per hour and per tile. The Brown house is the clear winner as to getting the most cash per hour. Tapping hundreds of Brown houses every 5 minutes is going to wear you down though. You do have to take into account the footprint of each house. The White house has the smallest footprint, so you can cram more into the space, than say for instance the Purple house which has the biggest footprint.
Here's a quick breakdown. Payouts for XP have a similar trend, at one tenth the cash gain.
Brown- $72/hr $2.05/tile
Purple- $25/hr $0.60/tile
Pink- $18.3/hr $0.46/tile
Blue- $18.75/hr $0.59/tile
White- $16.67/hr $0.69/tile
Orange- $15.625/hr $0.49/tile