I would echo the comment about the Italian greyhounds-- they are not very hardy. Their legs are so delicate. More hardy would be the Whippet. (the version of Greyhound size-wise between an Italian Greyhound and a Greyhound.) But this is not a dog I would let off leash. They are incredibly fast. Also, they can get very cold, too.
My uncle has had two different Bazenjis. I think that they are absolutely great. They are very smart dogs, so you have to get them excercise, or they will cause you all kinds of problems. They also have a little bit of an untamed streak lurking in them. Like the Greyhounds, they are a sight hound. As such, they are not really good to let off leash.