I'm kind of partial to the herding breeds - they are super-smart, but also high-energy. They also tend to stick around - if someone leaves the gate open, the worst thing my dogs will do is wander around to the opposite door to see if anyone is there? My current 2 dogs are Aussie-poos - the poodle cross tends to slow them down a bit and makes them friendlier.
But 2 smaller breeds that I've learned to love: Bichons and Shih Tzus. They seem friendly, intelligent, and loveable. Great companion dogs!
If you go the rescue route - if you're not well-versed on dog conformation or traits, take a friend who is. Because I've seen WAY too many rescues who are labeled as some pretty improbable mixes - and any idiot can see that they're pitbull crosses. I'm not saying that pits can't be great dogs - but there's extra liability that comes with owning a bully-breed. You might not be welcome in some RV parks; or your homeowner's insurance might not cover you?