I've got a Plummer Terrier (nose dominant) a Jack Russel (ear dominant) and Russel/Plummer mix that is a born earth dog.
The earth dog loves tight places, she actually craves fitting her body into the smallest possible area. She has a really flexible back, where the Russel and Plummer are kind of stiff in the middle.
The Plummer is a stone killer.
The Russel brought the wife a freshly killed 8 inch (without tall) Rat the other morning. She sat there with the Rat in her mouth, very patiently, waiting for the wife to finish eating breakfast. Or maybe she wanted to trade some Rat for some eggs.
With a Terrier around you don't have to worry much about rodents in the garden, they don't last long.
Terriers can be hard to socialize, they tend to be fighters by nature. It is always better to work them with a Dog of the opposite sex, it helps avoid conflicts.
My gun dog by contrast is a coach potato, until you get him out into the field. Terriers tend to be high energy all the time, they also tend to bark a lot.
I know some guys with Patterdales, the ones I've seen tend to be more antagonistic than a regular Terrier (if that is possible).
Most of the Brittany Spaniels I've know are lovers. not fighters. Good family dogs. Some seem a bit over bred and a bit neurotic at times.