Very personal preference but I don’t like the looks of the 18.
The 18 expy & navi do have some very nice features and updates that I wish the 17 had. Would also be great to have the ten speed. But, conversely, the 17 is an extremely well vetted design with the benefit of years of refinements and improvements. The 18 and maybe the 19 will have growing pains as the kinks are discovered and ironed out.
As someone who had tahoes and suburbans before this expy, I looked carefully at the next gen suburban as well and didn’t like it either. Without question Ford has a superior product than GM with these new trucks.