I'm late to the party, but let me say this... the pet that "speaks" emotionaly to your mom is the one. I've always had pets-from hamsters to my 100-lb. rottie. No animal is perfect, just as no person is. But the one you love, the one you "have to take home no matter what"...is the one you keep.
Each animal is different. Some dogs will be harder to train, but easier to love. Some cats are cool and indifferent, and others will purr in such a way that you never care how much they shed. For some people, the way a guinea pig sprawls on your lap with careless pleasure is the best pet.
I guess what I mean is that pets are chosen for emotional needs, in most cases. So "love at first sight" counts for a lot. The pet that begs to come in to your home, the one you simply cannot leave behind, is the right one.
I have a 60-lb. pit bull, two kitties from the pound, and two guinea pigs. Love 'em all, for different reasons.
And as far as dogs go, there are many rescue groups who carefully evaluate pets before adoption. Others do not. We attempted to go through a shelter, and ended up with a dog that bit one of my sons (not badly enough to need treatment, but unprovoked). We found our current dog from a breeder. He's not perfect - has ripped apart his kennel several times because he hates to be left alone - but completely loves all of us, scares away intruders, and adores my 2 younger sons even though they stomp on him when given a chance. He will always have to sleep in a crate, and is tough on our guests, but he's a happy, loving clown. The wagging tail and relentless desire to "kiss" everyone has won him his place.
Love is never wasted, and pets are well worth the trouble. Choose the pet that adores you.