"F-8P has two ventral fins and Mirage has only one. The Mirage has larger and probably better vertical stabilizer."

 

Ventral fins are used to supplement the vertical stabilizer in providing lateral stability.  So in that sense the two designs probably work out about the same.

 

As far as which is the better dog fighter, it would be shocking if the French hadn't figured that out a long time ago.  Although, the F-8E(FN) and F-8P pilots were pretty much experts in WVR tactics, so I would tend to give them the edge.