I grew up with a cairn terrier. We got it after my dad had been to a meeting somewhere, and the guy was dog-sitting this dog in his office. My dad fell in love with the dog. It's a lovely breed, and I have noticed quite a few people getting cairns now. Our cairn barked a lot and he wasn't too keen on kids coming into the house.
My parents now have a working spaniel. Spaniels are lovely too, but completely different from the terriers. I personally prefer the mild temperament of the spaniel.
Their working spaniel needs hours and hours of exercise and training every day. And 10-15 minute walks every 6-8 hours. They can't skip the exercise, as she'll be bouncing on the walls.
We have a show cocker, which is as mild and lovely as my parents' spaniel. But she requires far less exercise - she's fine with 30-45 minutes of training/exercise as well as the normal walks (10-15 minutes every 6-8 hours). Sometimes she gets more, sometimes less - and she's fine with skipping the exercise some days without bouncing off the walls.
I've found that the cocker is very easy to train, mild and happy. She loves kids - all of the kids in the neighbourhood know her and run over to kiss and hug her when we're outside.
As a bonus, she doesn't bark.
She's a velcro-dog, but loves playing - throw a ball, and she'll get it for you!
The cocker might be quite pretty to look at (especially if looking at show cockers ready for the ring), but they are hardy little ones. Mine might be a bit stupid, but she's happy to run through brambles to retrieve a ball. Not a girly dog at all.
My parents dog-sat our dog for a couple of weeks last summer, and they were so surprised that our dog requires so little exercise compared to their dog.