Which is the best of the n series,I got some advice that the korgn264 was a great keyboard,this has opened my curiosity on the n series.is the N5EX better,does it have a disc drive and a built in sequencer.same question for the N1.peace

Having a disk drive and a sequencer doesn't mean a synth is better that the other. The N264/364 is an older model than the N1/N5. The N264/364 is workstation oriented, wich means you have your basic sequencer and a storage unit for your creations. The N1/N5 synths are more "Performace" oriented, no seq, or disk, but you have the most usefull functions on top for playing live. ie: transpose, split, assignable knobs, etc...
I guess it all comes down to the requirement for you. (Playing live?, or Studio work?)

Hope it helps.