What do you call a person who always has a pleasant smile on his face?

I think this question really should have more context; it depends on whether or not the smile is genuine (and, if it is, it depends on the source of that person's happiness.)

If the smile is phony (that is, the person always smiles, but in reality, they are very bitter on the inside), then I'd call that person plastic, or saccharine.

On the other hand, if the smile is a sign of the person's pleasant nature, there several words that could be used to describe the person, depending on that person's source of joy and contentment, including: joyful, pleasant, happy, cheerful, and jocular.

Is there anything better than calling him a "Pleasing personality"?

One thing is certain, however, I would not call that person a "pleasing personality." You might say, "He has a pleasant personality," but a pleasant personality is something you have, not something you are. Moreover, a "pleasing personality" could be misinterpreted to mean that this person is predisposed to pleasing other people, rather than that this person is constantly smiling.

I think of such people as affable

Consider:

Happy-go-lucky
Cock-eyed optimist
Hail fellow well met
Devil-may-care
Slap-happy
Carefree
Lighthearted
Blithe
Village idiot

I would use amiable, which means, per Webster's Collegiate Thesaurus (1988), "of a generally agreeable nature especially in social interaction". Other options are good-humored, good-tempered, good-natured, and (rather rare these days) complaisant. All of the synonyms for amiable I've listed come from that same thesaurus.