Personally I don't want my sewing space separate from the house - it makes me feel isolated. At the same time, I want doors I can close off, so if I'm madly sewing away and DH wants to watch TV we can close the noise off (in both directions!)
But space is a big consideration, for me at least. I have a lot of sewing "stuff", including a sit-down longarm that comes in a table that's over six feet wide!
So, I'm not sure what to recommend - it's really going to depend on you and how you do your sewing, and how much "stuff" you've accumulated. It's wonderful that you have options, though!