I think Walter Mashburn is the most likely to be Red John. He has money, power and connections (to get into the CBI network for example). Jane has been told a couple of times that they are very much alike (by Rebecca and Lorelai): they're both charming and manipulative. They shook hands too.

The clues given are the followings:
1)Red John is most likely a man;
2)He appears to be a Caucasian, and is a white person as described by Haley:
3)Red John has an average height: Rosalind described him as "just under 6 feet tall";
4)Red John has short straight hair (as described by Rosalind Harker);
5)Red John either has or puts on an odd, high pitched and soft voice;
6)Red John should be older than 30 years (since his murders date back to the 90's).

1)Mashburn is a man.
2)Mashburn is Caucasian and white.
3)Mashburn has an average height.
4)Mashburn has short straigt hair.
5)Mashburn has a soft voice.
6)Mashburn is older than 30 years.

Also, in 1x11 Renfrew writes on a wall "He is Ma" with his own blood just before getting killed by Red John. The last letter is not clear, but it could be a "s".
John seems to have an interest in Lisbon too, in fact he asks Jane for her head in the season 4 finale; in 3x07 Mashburn sleeps with Lisbon.

If Walter Mashburn is not Red John, then my alternative is Virgil Minelli.