I like Capital Grille for the dry-aged porterhouse and the clubby, politician-heavy atmosphere. Charlie Palmer Steak is good, too, but it's more of a modern, not-just-a-steakhouse steakhouse.
Depends what you like.... Capital Grill is my 2nd favorite steakhouse in DC, and i m not really a Capital Grill fan. If you want a traditional steakhouse menu with the classic sides and nice list in a booth, CG. CPs is a bit more pricey, but has a lot more options on the menu.