Hands down. With today's modern sport motorcycles, the R6 has everything a rider could need to go from a budding beginner to a seasoned track rider. You just cannot go wrong with a machine that Yamaha got so right.
I just sold it late last week because I'm trying make good with my word, starting from doing less trackdays and into having just one bike in my garage. I tried to accomplish the latter last year with the Aprilia, but that ended after I totaled it at Buttonwillow. About a year later, I think it's time to try again.
I KNOW I'm going to miss the R6 on the track, but it was such an awesome machine that it gave me the experience and confidence to ride around the track on any kind of machine, even if it's a literbike.