It is Ray!!Why?Just read it:

We have clear evidence to know who is Red John.So why are we do not follow them?Throughout the series we got a description of RJ and if  we compared it with Ray....That's what we have:
1.Rich, influential member of the sect vizualist and therefore may be a manipulator
He has many friends and people who can help at any moment.Rather, vizualist is cast,which help RJ
2.Average growth, not loose body, a pleasant voice, short straight hair,his age
3.He likes to whistle
4.Cautious, reserved, secretive
5.Close to Teresa and this is important for him

+It can be only him.Simply by using the method of deleting,we can say that
Stiles:not suitable for age of RJ...He knows who is RJ ,but can not tell,cause it is person of his business
Bertram:not suitable for  the description of all
Sheriff:could be,in third episode we were confused...But his is not suitable for  the description of age,appearance, body and he  seems not so smart
Smith:assistant of RJ people(group)

It is all)