I have a 2017 RTL and while it was in the shop, the dealership lent me a 2018 RTL, I have also ridden my mates 2014 RTL
Disclaimer - there can be huge differences in the way they come from the factory and the dealership pre sales work to affect the what you eventually ride.
I found the 2018 auto adjusting suspension impressive and I became intrigued at how good it was at adapting to the road conditions (I did a 4000 km road trip on it)
My mates 2014 is just was smooth to ride, and I couldnt see any major difference in the handling between to 2014 (12000kms), 2017(15000kms), 2018 (450kms).
I was concerned that the dash on the 2018 would be problematic and I wasn't a fan of it, and a number of owners locally report issues with the phone app integration.
I don't think you'd go wrong getting a good 2015 RT, I think tide comfort would be as good, maybe not as "sassy" as the later models.