Both are correct, but "드십시오" is more natural.:) And "먹읍시다" and "듭시다" are correct. Here are other variants. 먹다, 드시다, 잡수시다(dictionary forms) 먹어요, 드세요, 잡수세요(informal) 먹습니다, 드십니다, 잡수십니다(formal) 먹었어요, 드셨어요, 잡수셨어요(informa, the past form) 먹었습니다, 드셨습니다, 잡수셨습니다(formal, the past form) 먹읍시다, 듭시다, 잡수십시다(X) \^o^/