I dont think any other show has kept up the quality throughout its series like The Wire. There are no throwaway episodes and it's never boring.
The Sopranos have boring seasons, so there's no way that can be at the top of the list.
Oz got too crazy and retarded toward the end, but the earlier stuff might make the list (not number one though).
The Wire is the realist show on TV and the best written probably ever.