I currently have a Delta DJ-20 with a mobile base. The unit stays pretty much still. It is a parralellogram with the handles for height adjustment. The fence support is center mounted which I consider a requirement not just a plus, but even though it is cast iron, there is a bit of deflection with heavy boards. Getting the fence square to the top at times can be difficult. Let's see, what else. 1.5 HP motor can be wired 110 or 220. Push switch, not magnetic, and it doesn't include the dust collection fitting which is a rip off if you buy it from Delta. Better to go to Woodcraft or Klingspor and buy a plastic bolt on for $20 less.
Overall, I am happy with it. I had a 6, and for anyone that is active in the hobby/trade, I would recommend getting a 8" as the difference is substantial for using it in flattening boards.