Should i get a beagle or a chihuahua or a cavalier king Charles spaniel?

I love all three dogs,I am away six hours every weak day and will be able to spend several hours a day with it, and wile I am at school my dog will be left alone with my pet cockatiel. What is more loyal? What is more intelligent? What is more trainable? What is more affectionate? What will really bond with me? Will it try eat my pet cockatiel,or benefit from its company?