Kennedy is terrible, and always has been. Samoa Joe hasn't been inconsistent, just exposed for the average worker he really is. Batista has been very solid all year long, and has had a very good year. Punk and Hardy I wouldn't say have been inconsistent at all, but rather have been consistently impressive. Out of these guys, my vote would go to Joe.
I would say the most inconsistent all year would be Randy Orton. You never know when Randy will turn in a good performance or bad, good interview or boring, if he'll be main-eventing or be sent home. I would say my overall vote would go to Orton.