Tough choice!!
I have a chihuahua, a rescue. He is the most devoted, loving, intelligent fellow I have ever met. (This includes my DH

)
But he is high strung. Part of that is the breed, part of that is what happened to him before I rescued him

.
I dont completely trust him around other people, but when people come over, he puts himself in his box!! He doesn't trust himself either!!
He is easy to carry (he is under 8 pounds), healthy, and his poop is little!
He sleeps on the bed and nestles up to my back at night!!
But most important to me is that he will live a long time. (God willing!) It is so hard when your animal companion passes away--I don't think I could handle that heart break too many times.
Good luck on your choice! And maybe consider a rescue--they know from what you have saved them and thank you every day!!
Cathy