I have the 16x18 ncode 95 and love it. I have tried the 18x20 and I am not sure that I would agree that it swings easier, I hadn't noticed a difference.
It could be mental, but it felt like the 16x18 had a little more pop than the 18x20, but both are solid racquets that are equally suited for baseline and volley play. Overall, I don't believe that there is a drastic difference. You can generate a solid amount of spin off both variations, control is pretty close and serving is great.
I play the 16x18 because I like the little bit of pop. I play doubles and it helps for my kind of serve and volley game. If I played more singles, the 18x20 probably would be fine.
On another note, the 16x18 seem to be much more popular and therefore the 18x20 usually sells for less money on the used market, IMO.
Hope this helps.