Standard bike has Sachs suspension, so does the six days bike. Racing has ohlins suspension. Six days bike and the racing edition have the 2k-2 ignition which has a lighter flywheel so it revs up quicker than the standard EC.
Six days bike has white plastic, racing has different graphics and comes in either red or blue I believe.
Personally I'd get a six days bike if you can. The lighter ignition is great and the sachs suspension is amazing. I have an 07 Six days EC250 at home that I thought was great, but the new 09 I rode at the ISDE was better. The suspension was great, the new seat is awesome and they changed the shock mount position so the bike handles a little better.