N1, N2 and N3 tyres are the sort of tyres you see on real cars on the roads. So N3 is probably close to Bridgestone Potenzas. N1 is probably those POS tyres Kwik Fit give you.
N3's are more your standard Bridgestone tyre for your normal car where it's good but not great. N2's are for more upper class cars I've noticed (say a Continental tyre) and N1's are your good old retread!!
On a sports tyre front, I look at it like this:
S3's are more like the Pirelli P Zero tyre.
S2's would be like the Pirelli P6000's.
S1's would be like the Pirelli P3000's.
...N2/N3 are the closest match for the standard tyres on an M3, info released with GT5P also backs this up (with the exception of all Japanese performance cars getting S1 or S2's - but that may just be a bit of bias).
This threads locked, the other one is fine for carrying on the discussion.