I've had both the 14 way (in my previous SD) and now the 18 way in my GTS. I find the 18 way far more comfortable (and my regular passengers concur), esp the side support which I think is lacking in the 14 way. That's not to say the 14 way aren't comfy by the way.
So best advice to anyone trying to decide is to test out both 14 & 18 way as it's obviously down to personal preference.