I had a Jack Russell Cross. He was the coolest frikken dog ever. Yea, he'd get excited and sometimes piss me off, but he was soooo happy to go fishing it was a joy to watch him. I'd tell him we were going fishing in the morning and he knew it when we woke up it was time to go. You could read the expression on his face. THe nice thing about this type of dog was his size. He was 30 lbs, so a fair bit bigger than the smaller jack russels you see. Plus he was super agile, so if we were hiking into the canyon or over boulders etc. this dog could handle it no problem. Now I have a duck toller. She's a super water dog, the only problem is she wants to be in the water a lot so sometimes she is spooking fish. This dog is only 34 lbs.
My advice would be, get a dog that has some energy. It's fun to watch them get all frieked out, then you bring them home and they are good and tired for a few days.