Timon and Pumbaa aren't my favourite characters of the Lion King universe (Simba is) but I have to say that if I had to decide it would be Pumbaa.
Pumbaa is one of those characters who you love no matter what. He is loyal, kind hearted and a good friend no matter what, even if he is misunderstood. Compared to Timon who isn't really a good friend (his constant stealing of Pumbaa's ideas and his initial rejection in The Lion King:Hakuna Matata).
Pumbaa has never swayed.
(I also like Zazu).