I've been getting on well with some Metzelers. Got a Z6 on back, went on July 2013 and has done about 12k. Bit squared off, but still a couple of mm of tread left. On the front I have a Z8, which went on about a year ago, done around 7K and has plenty of tread left. Both have given me decent grip. Z8 was definitely an improvement on Z6, albeit around £20 more expensive.