Unfortunately, those breeds aren't really known for agility work. I'll bet there are some Rotties, GSDs, and Beagles that do well in agility, but the main breeds to look into for that activity are Australian Shepherds, Border Collies, ACDs (and other herding breeds or mixes that are relatively small and quick), and some of the terrier breeds. Watch some agility shows on Animal Planet and you'll see what I mean.

Any breed of dog can do obedience if s/he is trained right--although I have to say that my first dog was a beagle who made a complete fool of the professional trainer she had! Some dogs are just more independent than others, and won't bend over backwards to please you.

A warning about those herding breeds I mentioned, though: they need to be BUSY ALL THE TIME. They are scary smart, very energetic dogs who'll turn into nightmares if they're bored. We have an ACD mix and an Aussie, and their stamina is amazing! They're extremely easy to train and a joy to be with, but they definitely need lots of time with us to be happy. So many of these breeds end up in shelters and rescue because people have no idea what it's like to live with them.

Here's a site with good links to agility info if you're interested: www.dog-play.com/agilityl.html

Good luck!