Well, I know about Dachshunds and Australian Shepherds and Australian Cattle Dogs. My dad just adopted an Aussie pup and I've done tons of research on them. And I have owned to Mini Doxies in the past which I'm pretty sure temperament is the same as the full size. And I've also had an Australian Cattle Dog.

Dachshunds:
Sweet and adorable, these make great dogs only if you have a fenced in yard or they are leashed. Number one thing with scent hounds is... They're brain shuts off when using their noses. They will follow a scent and may get lost, not to mention the many dangers for a dog to be out alone in today's society. They are not very easy to train, (potty train specifically!), so plan on working with them A LOT with that. We were never able to potty train our two mini dachshunds... course it was probably our fault not theirs. Other than those things, these are wonderful little dogs. They are very happy and tend to be quite friendly with people if socialized well as a pup. They can be barkers.

Australian Shepherds:
I'm sure you know, these are highly intelligent dogs!! Basically the geniuses of the dog world. They are very easy to train. Unfortunately, intelligence also comes with easily being bored. These dogs need PLENTY of mental stimulation throughout the day. They are very active dogs. They need lots and lots of exercise. If you do not plan on having a "job" to do with this dog (whether it be herding, frisbee, agility, etc.), I would not recommend it. My dad lives on a farm with our new Aussie pup, he will have plenty of room to run around and we also plan on having him as a therapy dog. (my dad directs a nursing/assisted living home) They've got medium length coats that are quite thick, and they need weekly if not daily brushing. They do shed quite a lot during shedding seasons (spring and fall). As long as they have the mental and physical exercise they need, these dogs make wonderful pets. And they're absolutely beautiful too! They are known to be aloof, but polite, with strangers.... so they need plenty of early socialization to people, places, and things. These dogs get very attached to their owners and follow them room to room. They are not meant to be left outside.

EDIT: And they LOVE to herd. So if you have small children, you've got to teach them early on that they cannot herd the children. They need to be taught that they cannot nip at human's ankles.

Australian Cattle Dogs:
These dogs are much like the Australian Shepherd, but in my experience, are a bit more intense. They need tons and tons and tons of exercise. Better yet, it is almost mandatory that they have a job to do. Simply jogging them in my experience just isn't enough. They are very easy to train, they're a crazy smart breed. My mom's boyfriend has a red heeler, and she seems to not have the energy my red heeler had. So it may depend on whether they were bred for work or show. Plan on spending plenty of time with this dog, getting enough exercise and mental stimulation. They are extremely loyal and loving pets. This is a great breed for the right owner. They also need a lot of socialization.

Unfortunately, my dad got an Australian Cattle Dog without fully researching the breed. (I was very young at the time) At the time he did not have the room or the time to exercise him (Buddy was his name), and we had to give him up because he had too much energy and became very destructive. A friend of my dad's lived on a farm and took him in, and he herded cattle there. I got to see Buddy a lot after that and he was a great dog.

Anyways, good luck on your breed searching. Its great that you are getting the information before choosing your breed. I'm sure you'll find an awesome companion