which traits they carry from each breed, but Jack Russell's are notorious biters because they were bred to be hunting dogs.
I have a Jack Russell mix and she was 1 when we rescued her, so she already had a lot of bad habits. I took her to Pet Smart training and normally I'd say Pet Smart or Petco are not great for training, but they really are dependent on the trainer you get.
Our local Pet Smart had a trainer whose full time job is training service dogs for military and police. He was excellent and worked with our goals which were:
1. Leash training
2. basic commands, sit, stay, leave it, lay, take it, etc.
She was already crate trained and house broken.
he helped us through that and now as a 3 year old she's an incredibly well behaved dog. Only thing we haven't trained out of her is cats. She still and will probably always go absolutely nuts when she sees a cat. She almost crashed through a screen in our house trying to get at a cat in our yard so I let her out in back and she jumped our at the time 5-foot fence. and she caught it and had it pinned before I could get there and free the cat.
So my advice would be check out your local petsmart or petco and ask if you can meet the would-be trainers. Cheapest and in my experience best way to get specific training.
And for he record, we had hired personal trainers who came to the house initially and they sucked.
Here is a picture of Rosie (distorted through picasa app, but only picture I had on my phone). she's 25 pounds of muscle, but very gentle, playful, and safe.