@ Track_ Fanatic: Yeah, admittedly I had the same problem, the last Track ball I absolutely loved was the GP2. Wasn't a big fan of the original stuff Track came out with when Ebonite first purchased them. As well, I was very wary of Ebonite equipment considering my personal horror story with the Gamebreaker, but I must say the stuff they are making now is pretty amazing.
I won't say every ball is a must buy, I think the 706A and 300A are just average balls that fit in any arsenal, but nothing special...but of the new stuff the 503T and the 912T are just special balls.
@ Everyone else: As far as old balls, I mainly used the 920A and 920T as a 1-2 combo all summer long. I actually un-loaded the 916AT and 505T to a couple of kids who made their high school bowling teams about 2 weeks ago.
I typically prefer to wait for stuff to get discontinued and buy equipment I know is proven, but I am probably going to be making an exception for the 503T, 912T, and Violent Eruption.