My theory is that all the 8 person  ine RedJohn list on 5th season last episode are RedJohn disciples and maybe on of them is RedJohn. Maybenot. 

Bob kirkland is definitely disciple, the photograph he got from jane's room helped the RJ to figure out who are all on the list. this is already clear. he kills that other RJ disciple in hospital also. a work usually assigned disciples.

Gale bertram is already disciple because RJ is able to figure out what is happening inside CBI. there is not more better way than bertram to do this.

Ray Haffner is the guy who painted RJ smiley on the barn run by visualize. he is gonna start a new security agency. he is definitely one of the disciple. and one possible suspect of being RJ.

Reed Smith: This is a viable suspect for being RJ. because he appears not so many times before us and in many cases is being fooled by Jane. so I am not reading RJ or Jane here. I am reading Bruno here. I am expecting a double bluff by him here. because we all expect a non-famous guy as RJ. but I am thinking he will put popular guy as RJ. so i am crossing down reed as RJ. but definitely a disciple I guess.

Mcallister: This is a viable suspect for RJ, but only seen in one episode. more age than expected. I am expecting RJ to be same age as Jane. but over secrecy of mcallister make give him high rank to become RJ. I am keepping him as RJ suspect. 

Brett Partridge: He is also definitely a disciple of RJ but not definitely RJ. because in the first episode he identifies a non RJ murder as RJ murder and other one in second season. if he is RJ he will not be willing to give RJ trademark to other mans murder. RJ is highly sensitive like that lot of self pride. 

Bret Stiles: This is the highest ranking suspect for RJ in my view point. because RJ is same as Jane. a psychic capabilities may be more than Jane. Brett stiles can manipulate minds make disciples to follow his order stiles has shown this capabilities one or two times in other aspects also.  Jane at some point is tranced by stiles to know some of the secrets of Jane. like the murder in last episode. this is why he knows jane's secret. So bret stiles is the highest ranking suspect for being RJ.

So my Red John Suspects are in its ranking

Bret Stiles
Sheriff Mcallister
Ray Haffner