I've heard the Metzler is a softer tire so it doesn't last as long but grips the road better. I've got just over 10K on my sock tires and probably wouldn't change the front yet but it's got a slice across the middle so better to do it know, the rear still looks pretty good might get a another 2K or so out of it.
I recently replaced the front with a Metzler. I think it is much smoother, stickier and doesn't grab the grooves in the road nearly as much as the Dunlop. I think the consensus is that the Metzler rear doesn't last as long as the Dunlop. I am going to try one anyway to see for myself. I have always tried to shy away from Dunlop in the past, but the stock rear hasn't treated me bad at all.
I don't care for the factory Dunlops. I love Shinkos but I couldn't find a 200/50-18 so I went with a Bridgestone Battlax. Much stickier than the Dunlop which would just spin through first gear. The Battleax really sets you back in your seat on those clutch dumps.