For me, it really depends on what you mean by cost and space. If cost and space weren't an issue, I'd have to have a dedicated brewery room. Strictly for brewing, cleaning and fermenting. If that were the case, I probably would have a 3v system. Right now, I don't have a dedicated brew space, it's shared with the laundry room. And even though I do have room for the 3v in there. It's not set up how I would want it to deal with the extra cleaning that would go along with a 3v system.
So yeah, if the sky were the limit on money, then I probably wouldn't use the grainfather. But, without that dedicated brew room, I think a 3v system, although theoretically, have the space, would be in the way of other chores that have to be done. So I would have to move things around and worry about people putting stuff on it or in it's space. The compactness of the Grainfather really is a bonus. It's easy to just move it where it needs to be and move it out of the way, when other things are going on. I have too many other things that need to be done and paid for though, before a dedicated brew room would be in the cards, so for now, it's the Grainfather all the way for me.
The best part is if the laundry room is being used, then I can go to the kitchen. If it's a nice day, I can go outside on the patio or in the garage.