Papillon Or Chihuahua, Which Should I Get?

I want a smart dog that can be trained various tricks and I would like one that enjoys walks and playing but is not constantly craving walking and playing. It is important they would get along with another dog an that they are ok with children even though there are no children in the house. Also, it would be left along whilst I work full time during weekdays-but-it would have another very small and friendly dog there, plenty of toys, water and access to the garden.
Which do you think?