A very good question. Awesome cars, but the AWD adds complexity, weight, and maintenance costs. I kind of prefer the way the GTI handles. The R is almost too polished. The 2018s have the 6Y/72M B2B warranty which is what I'd want, but also comes with hideous (IMHO) 19-inch wheels which I'd bend in the first winter (I'd have to get dedicated winters for sure) and little to no depreciation. Seems like the few used 2018s are still in the high 30s. Oh I also very much prefer the analog gauges in the GTI versus the R digital gauges. I guess I'm old school in that way. I really have my heart set on the plaid seats, too. But I am keeping an eye out for a gently used R. I think it mostly depends on where they price the 2019 Rabbit Editions and how much they discount them. A new 2019 GTI S will be under $25,000 after discounts, so that's a far cry to $35,000 for a used 2018 R for a daily driver.
Alot of cars are speed restricted to the speed rating on the OEM tires.
Porsche/Audi/MB/BMW all agreed years ago to limit regular production cars to 155mph. Limited production and M/RS/AMG cars are not included in the agreement.