Monolevers are my favorite airheads.
R's? I am not personally a Paralever fan. They make the wheelbase too long. They weigh more. The drive shaft U joints are more likely to go bad. The driveshaft rubber cush-drive is way more likely to fail over the spring/cam setup on a Mono. The final drive input shaft seal is very likely to leak leading to drive shaft rubber issues. The tranny output seal is too to a lesser degree. The paralever bearings wear out on a very regular basis. But they do have less drive shaft effect. I grew up riding beemers so I am use to that.
And then there are the R's forks. If the forks don't already need new tubes for flaking and pitting chrome, they soon will. I don't understand the need for a rubber mounted fork brace? I love that they have teflon bushings for less stiction but they do need to be replaced on a regular basis. I would say about every 40K miles.
I have always liked the looks of cross spoked wheels but I did not realize until recently that they are even heavier than the Mono's wheels and the mono's wheels are too heavy IMO. That and the cross spoke wheels are rarely even close to straight right our of the crate!
Plus I like the looks of the Mono's better but that is just me.