Every now and then a psycho JRT pops up, mostly (but not always) when they're owned by people who don't understand the breed. A JRT is not a lap dog - it is a hunting dog, and must be kept mentally stimulated. Also, they have extremely strong dominance instincts, and will be alpha dog or go nuts trying.
Treat them right, and you have smartest, most loyal, and most affectionate dog in the universe. The is a reason, though, that they're nicknamed Jack Russell Terrorists.
It strange, Amstaff owners I know would say the same thing!
Being around both I am struck by the similarities between them.
A small dog doesn't fit my life style right now
but I can see as I get a bit older and slow down
that a JR would be a very desirable companion dog.
One thing JRs and Amstaffs seem to share is an uncanny ability to perceive precisely the time to lick to coincide with that off guarded moment when your mouth is open a crack.