Having seen both of them in action(Karthick in England) and Parthiv in Australia 2003, i can safely say that Karthick is a more nimble and fleet footed keeper than Patel...
Karthick has far superior reflexes and also has a very safe pair of hands...
As far as batting ability goes, there are reports in some quarters that put Patel as a better batsman...i don't think so!! Look at the way Karthick played in England in 2007...he was the highest run scorer on seaming tracks...so this theory about Patel being a better batsman has also been promoted by freinds in the press...as simple as that!!
My vote goes to the dynamic Dinesh Karthick who will bring glory to India in this series!!