I don't want to vote for Mario because he was such a success all over the place. Indisputably one of the top 5 all time greats.
Zanardi accomplished a lot very quickly, but I think if he'd stuck around longer that the average would have been lower. He was certainly good, but I don't think he was better than several other drivers who were racing at the same time. In his best year the luck always seemed to go his way. No matter how dumb of a move he'd make, somehow it would out for the best. Often he made passes through being too agressive and forcing the other driver to back off if they wanted to finish the race. He almost killed Andretti through his recklessness. Also, VASSER beat him in his first year. What does that say?
Rahal was more about reliability than outright speed. I can't vote for him.
Mears to be honest I don't hold as much stock in some of those early CART drivers. Part of it is that I wasn't around so I don't want to vote on something I don't know enough about.
JV was very good in CART, but he never raised his profile substantially above those of a few other drivers who were racing at the same time.
I'll give my vote to JPM. I do not believe anyone has more raw talent than he has. He's a freak. Everyone knew he was king of CART despite incredibly poor luck in both years of running. Nothing seem to work out for him, despite being indisputably better than all. CART's field was also at its most competitive in this time period. I'd kind of a wierd vote because he didn't accomplish that much. I'm voting more on what he could/should have accomplished and raw speed.