Ah the Jack Russell Terrier, where do i begin!
I have experienced many breeds of dog in my lifetime and to be honest, the Jack Russell really stood out from the crowd. This is a dog with incredibly high energy levels and a constant need for attention. Probably one of the funniest breeds around, this dog is always getting up to mischief when you're not looking! Also, they are very intelligent dogs and, if given the time and patience, can learn a variety of tricks. The JRT is usually a stubborn breed on occasions which can make it difficult to get it to do what you'd like. Throughout this dogs life you will need to remain you're status as 'the boss' of the household because this is one breed that always wants to be top dog. Also with this breed, as well as any of the terriers, I would be cautious around letting you're dog loose in a very large place. This is purely because of their instincts and desire to hunt small animals and this can land them in a lot of trouble such as chasing animals down holes and becoming trapped or even running away and not coming back when called.
All in all, this dog can make a very loyal companion for someone who wants a cheeky little friend to keep them company. Beware to those who are looking for a cuddly little lap dog, the Jack Russell is not for you! If you make the leap to get a Jack Russell then remember the constant training because this is a very dominant breed and firm training is necessary otherwise you may end up with a dangerous dog.
You either love them or you hate them, personally I love them and i hope you do too :)