I went from the stock tires on my C50T to the Metzeler 880's and the FIRST thing I noticed was that they did NOT track in ruts. I was AMAZED at the difference. I will definitely get Metzelers when the time comes. To be fair though, I have heard a lot of people also liking the Pirelli's, so maybe compare prices on the two and go with the best price???
I've heard that Avon's are a nice, soft riding tire but they wear out kind of quickly, as do the Dunlop's. I would avoid IRC. They're not a terrible tire, but there's better out there, so to me they're not even in the running for replacement tires.
Are you going with stock sizes or +1 size in the rear? And just in case your next question is: "Where is the best place for prices"?..... Shop the Net then contact a shop that's convenient to you. You'd be surprised how competitive the m/c tire market is. Make sure you get the "mounted and OTD price" from the shop. Compare that to the prices on the Net for tires + shipping + mounting + tire disposal, etc etc etc... Lots of times for a matte of a couple bucks diffrerence it's worth the convenience of having your local shop do it vs. the hassle of ordering, waiting, transporting the tires to the shop, and doing all the leg work.
My $.02 and good luck with the shopping,
Daryl