Best summerslam match for Batista?

I agree with you 90%. Brock vs Batista(The Animal vs The Beast) would be, quoting HHH, 'Best for business'. This match would bring in a lot of money to the WWE and would be the ideal mainevent for Summerslam. But I do have 2 problems with this match:

Firstly that would be likely to mean that either Brock or Batista would be the WWE WHC champion, which I don't approve of. Secondly, who would be the face of the match, personally they'd both suck as faces(cause Batista gets booed soo much), so it'd better be a heel vs heel match.

I read that they're planning to have either John Cena or Daniel Bryan be his opponent at SummerSlam (CM Punk was considered, too, but since he probably isn't coming back anytime soon, that's out of the option). I agree on Brock Lesnar but since both of them are heels (though Lesnar is still popular compared to now Batista), that's unlikely. I would say Dolph Ziggler so that the confrontation they had a couple of weeks ago would continue in the future.

Brock Lesnar in a last man standing match

yes i also say brock lesnar infact i wanted them to fighting in wm 30.Unfortunately it didn't happen...

Sami Zayn.

I hope somebody brand new with uber talent gets pushed as quickly as possible.

Fresh matches are a good thing.