Not all terriers will be good at ratting. If you get out a lot with various dogs and people you can see it. Plus as with all other types of hunting, there are those that can do it, and those that can do it very well. And there is scrounging about for the odd rat, and there is ratting!
I've seen everything from bull/greys to dachshunds ratting. For me as a breed terrier wise, even though i dont own one, the old strain stocky plummers were good dogs on rats, i haven't seen any of the new whippety ones working so cannot comment.
And not being biased because she is mine but the best dog i hav