For me it has to be Rob Van Dam, he is the master of the move.
I always thought the 5 Star looked the most devastating of all the Frog Splash's that I have seen. The impact that RVD hits the move looks greater, he could get higher than anyone else, the way he bounces off his opponent after landing the move is great and the way he sells the pain after landing on his victim emphasis the damage it causes.
Also, he could hit it from almost anywhere in the league, and the fact that he could rotate in mid air to land at a totally different angle is unique and spectacular.
I was never really a fan of Eddie Guerrero's, Christian's or Jushin Ligers, but I have to give an honourable mention to D'Lo Brown here. His Lo Down was brilliant, and I have never seen any other wrestler perform a frog splash the way Brown did. The way he swung his arms below his legs made for a unique, and very cool move.
But RVD has this one in the bag for me, the Five Star Frog Splash is a great move