Mine is JRT... Mostly. I have to say that mine isn't for the faint hearted, and nor would he be anyone's idea of a model first dog. I've gone on a crash course in dog training and behaviour due to him!
He's lovely if he gets at least two hours exercise off lead every day. He's very not lovely if he doesn't get enough exercise. This is especially fun in the winter when the days are short (limited time) or there's snow on the ground - he can't cope well with cold weather. He's also not a morning dog and considers rising before 8am an act of cruelty.
He has a tendency towards reactivity - first it was motorbikes, then I managed to make great progress on that and so he seems to be replacing it with bikes. There was a stage when it was impossible to walk down the street without an incident. He's great with dogs so long as
a) he can get to them (otherwise he has historically become frustrated and barky)
b) they're not one of his two disliked breeds
c) he's not got something valuable with him (resource guarding; sticks are now banned!)
He likes few things more than a good game of chase / play fighting with an amenable playmate. He's also totally obsessed with balls.
He only looks genuinely happy when two people appear - funnily enough the two people who walk him. He takes his guard dog duties seriously. One flatmate of 7 months found himself treated like a burglar every day. My DGM has been feeding him under the table for almost a year, and is treated like a vending machine rather than with any genuine affection. Strangers are a complete irrelevance to him, and he invariably blanks anyone who tries to say hello to him. He's coped with a weekend with sensible and pre-briefed 5-8 year olds, but he was watched like a hawk.
However, indoors he's nearly perfect - sterling house training, no separation anxiety, never ever chews anything that isn't his, doesn't steal food, minimal barking etc. He's intelligent and learns things quickly.
If I could picture his perfect home it would be a rural home with no traffic, no livestock to chase, lots of squirrels, lots of dogs on walks but none in the house and lots of exercise. Ideally in a hot country... In reality he has an inner city home with me, but we get on alright! 
It would be almost impossible to fully work out what's due to his breeding, what was due to his early lack of training and socialisation, and what's just him. I think a substantial amount of it is his breeding, but I have no doubt that he would cope better with life if he had been socialised properly as a youngster. I love him dearly, and wouldn't swap him for the world, but if I'm completely honest I probably won't get another JRT in future.