I looked at some of the smaller ones too. They are cute, but we have two kids and a dog and I'm afraid they'd get tight on rainy days.
We now have a 34 foot triple axle and it seems just about right
The 34 really tows nicely too. It's long, so you have to be mindful of the length, but other than that, she tracks straight as an arrow.
Anyway, not to dissuade, but I'd have to go along with the guys recommending you look hard at a 25 footer.
As for new vs. used, my experience has shown that warranties are pretty much worthless. I'd get a decent looking used one at a huge discount and run with it. At least that way you KNOW you are the one doing the repair work, rather than making five trips to a service center to mook it all up and then you wind up fixing it yourself six months later anyway.
Best of luck whichever way you go. Just get out there and camp and have fun!