What's the difference between these two (apart from the £2 difference in price!)?
http://www.oponeo.co.uk/tyre-details/michelin-pilot-sport-120-60-r17-55-w-front-tl-m-c
http://www.oponeo.co.uk/tyre-details/michelin-pilot-road-120-60zr17-55-w-front-tl-m-c
The speed rating.
ZR is rated to 240kph+
Can your bike go as fast as that?
If so, buy that one.
Both tyres are 'W' rated, so safe to 168 mph. The 'ZR' rating is a bit redundant these days since the final speed rating is specified by the letter on the end.
The "Pilot Sport" will have a softer compound than the "Pilot Road", so more grip and less life. Those are pretty old tyre designs though, the newer 2CT Pilots that have dual compound tread are better.