Nitto-555R VS. Nitto-555

I'm buying either the 555R or the 555 by Nitto. The 555R looks like a better tire (performance wise) but my buddy said they are not worth the extra cash. Anyone on here used either? If so, please give me feedback positive or negative....

Well it doesn't look like i have much of a choice. My tire size isn't offered in the 555 only the 555R (315/35/17). I wish www.tirerack.com carried Nitto. Oh well, never mind.