The sp2 is a better bike generally. It doesn't have issues with leaking fuel tanks or radiators, and has nicer wheels and swingarm. Perhaps most importantly the sp2 has a ton more exhaust options. If you have an sp1 and want to put on a slip on exhaust, you'll more than likely need to purchase an sp2 header and slip ons for an sp2
This doesn't make the sp1 a bad bike (We will have a storm of sp1 owners in here soon screaming about how the sp1 is more "raw" than the sp2, but what they mean by that is it's poorly tuned from factory, the sp2 has a better ecu)
You won't go wrong with either, but if you can find a nice sp2 it is likely to be more problem-free than its older brother. You'll find that a large number of sp1 owners have put sp2 parts on their bikes.