A quality 6" jointer will do many tasks. The bigger is better syndrome comes from folks like me who do work that collides with the 6" restrictions. My 6" was perfectly acceptable for edge jointing but I can do that almost as well on the TS. It works fine for milling small lumber; table legs and stretchers, picture and mirror frame parts, small wall shelves, and small box parts can all be done on a 6".
If you want to stay with a 6" for space concerns, embrace it and don't scrimp on your features. As Bill mentions (and I can chime in here too) if you go small, don't go cheap; you'll just have to buy again and that's a false economy.
If you don't need the width, that's great but that is the only thing that should change. You'll want adequate power, good knife choices, long beds, great fence, reliable adjustability and good dust control. Fortunately there are several players in this field as space is always our enemy (it seems) and manufacturer's provide a solution.
Here's some examples but I would want to hear from owners and I'm sure some will chime in.
Any sufficiently advanced technology is indistinguishable from magic.
- Arthur C. Clarke