I've been raised by yellow labs my entire life, can't wait to get my own, but won't until I have a house with a big back yard, otherwise it just is not fair to them.
My other advice is to do research into the type of dog you're looking at. A lot of the smaller dogs fit into the toy category and obviously are solid pets. Some of the smaller breeds though are hunting dogs or herding dogs, thus have a lot more enrgy/endurance, and sometimes strange tendancies. For example, the only other type of dog besides a lab that my family has owned is a welsh corgi. Corgis are herding dogs – they are small, agile and tough as nails. We got her when I was four and for the first six months or so she would herd me up and down the halls, and all of the cuffs of my pants would have holes in them from where she would nip at my heels. How I hated her. In the end when she was broke of the herding instinct she was a great dog, very smart, and protective. Just something to keep in mind.