If you are looking for a dog that is easy to train and good at agility i think you should get a border colie. They are really good at
agility and they are smartest dog. If you watch dog show on animals planet sometimes they will show you a agilty. If you want to get a small breed that does agility good at I think you should get a Jack russell terrier they are pretty smart too. Boder colies are my favorite dog so I know lot about them if you want a smart dog and does a agility good at you should get a boder colie.