Should I prefer Farmers or other followers?
It sounds like you are pretty new to Carcassonne.  It's pretty easy to start playing and have your group think that nearly everything should be finished and the board should look nearly square at the end without many blank holes in the grid.

If this sounds familiar, then yes, there are likely to be big farms and its a good idea to get in early on the farm.

You could change your style though.  I view every meeple played by my opponents as something to be attacked and stranded!

When an opponent plays a farmer, that meeple isn't moving ever again.  You need a good reason to extend that farm in any way.  Play around it.  The next road juncture you play should be positioned to cut off the farm.  Do not play city tiles on the farm.  Just leave it alone!