Kisame would win via absorbing raikage's shield when raikage gets near him.
The only chance raikage has is to try and blitz kisame from behind, separate kisame and samehara without the use of his raiton shield, or one-finger hellstab kisame through samehara and pray to God that the attack will be to strong for samehara's absoption.
Kisame is basically the best opponent for people who surround themselves with chakra shields, and have jutsu that rely on said shield.
I'm sure kisame will also give a good fight he is one of the Seven Swordsmen of the Mist and he is described as a Tailed Beast without a Tail cox of his chakra
kisame will definitely win.. With samehada he will absorb all the raikage lightening chakra. As you can see when he's fighting with bee, the samehada is fast chakra absorber. Raikage dont have a chance, he will only try but at the end kisame will win..