There is really geat advice on this thread. Mine is: pick a breed that you enjoy and can live with. I started competing with an Australian shepherd and Whippet.

I currently have four dogs, 9yr Whippet, almost 6yr Swedish Vallhund, 4yr Siberian Husky and 10 month Swedish Vallhund.

We train and compete in Agility, Obedience, Rally and Conformation.
My older Vallhund needs one more major for his AKC Championship and is working on his AKC Master Agility Ch. title. He also has his AKC Rally Excellent title, UKC CH and agility titles in UKC, USDAA, and TDAA.
My Siberian had his AKC Rally Excellent and is working on his AKC CD and just starting in Agility.
My Whippet is retired and had earned AKC Agility titles and the Vallhund pup is just starting in Conformation showing and Agility training.

I am on my third weekend of Agility shows with one more and after that Conformation.
It is not just a hobby, its a lifestyle

Chase, Whippet - over the Rainbow Bridge:

Tripp, Whippet:

Scout, Swedish Vallhund: