I own both. Started with a '20 Laramie with ORG and air-ride. I bought that one off the lot and took what they had. I wouldn't have ordered either option, but I was pleasantly surprised with how great it rode. I am after the best ride as I age. Was in GM's forever, got a Ford and it rode better, I thought I was in heaven until I drove my '20 Ram. Wow it was amazing (to me).
So good in fact, that when I was back in the East and drove my '18 300, I was like "wow, that Ram rides better than my 300, go figure".
When I say ride good, a good ride to me means the least harsh over potholes and the like. The harshness of a hit is what I dislike as I age.
So I traded my 300 and my Ford on a '21 Limited that I ordered and spec'd it similar to my '20, everything the same except I now added the Safety thing to get the auto-cruise (needed in the East, not so much in the West). I was concerned over the 20" tires on the Limited vs the 18's on my '20 Laramie, and if it would add to any harshness. It did not. As a bonus with the ORG, ya get the very good Falken's and the locking rear, needed in the West, not the East, although I used it already when we got 30" of snow last winter in the East to get in my driveway that the plows had built up about 20" when I got home. I was also able to raise the truck up the highest it would go, which I'm confident helped me through the 20", but I'm guessing the locked rear was the biggest contributor.
And there are way more potholes in the East than the West. If I had to put a number on it, I would say the 20" tires are about 10-20% less forgiving than the 18's, but it is still Soooooo good I haven't enjoyed a better riding vehicle in over 20 years since my last Buick Park Ave.
Best of luck.
As a side note, one thing I can't explain is the Laramie with 18's handles a little better than the Limited with 20's. It is noticeable. Handling as in going around fast turns. I've tried different pressures in the 20's and nothing works. It is opposite you would expect, but it is what it is. Maybe it's the Limited rides a little higher as someone said above, but I don't notice the added ride height much at all.