Sharon's absolutely right, Carolyn.
I think you need to decide what you'd feel comfortable with. Many RVers have small dogs because they think that they're better suited for the smaller spaces in an RV. But I have a 75# Lab and wouldn't think of having a small dog. It's all personal preference.
One thing I do know is that small dogs tend to be more ... vocal (trying to be nice here
). Jed's not a barker unless he perceives something's not right, so from that standpoint he's a good watchdog. And he's big, which could be a deterrant if necessary. But he also requires regular exercise and sheds like crazy.
It all depends on what you want, what compromises you're willing to make, and most importantly whether you're willing to take on the financial responsiblity of a dog. I don't believe that bigger dogs are more expensive, except for the amount of food they eat. Health-wise, little ones can be pretty pricey sometimes, too.
I wouldn't trade Jed for anything, and am grateful for all the love and joy he brings me. And everyone who has a dog would say the same thing.