I've always liked him more then Timon, to be honest. Pumba seems to be much more kind and understanding, and also he's the first one to suggest taking Simba in, as well as going to Pridelands after him. He is often the voice of reason for Timon, even though he's too... I dunno, dependant on him, to speak his opinions loudly.
He is physically strong, and that's also helpful on several occassions, like when he drags Simba after he is hurt after Zira ambushed him. Kiara and Timon couldn't have done that!
As for him being stupid. Well, I personally disagree - if anything he felt somewhat naive and childish to me, and a little selfless.
His fart jokes don't bother me - and I don't think it's his sole purpose either, because if we take them out we'd still have a lot of Pumba left.