Vocabulary.... and then as much kanji with them as possible. EDIT: it shouldn't be a "A or B" kind of question. you need to learn both. learning ONLY kanji does not make sense, but learning kanji with vocabulary helps you to avoid mis-associating some words that sounds the same but mean different things... or realising that some of the words that sound different are the same since the kanji is the same.

My answer is "both at the same time". Most of words are spelled in Kanji, so you should memorize in Kanji. For example, we have a lot of "こうえん"; 公園、後援、公演、講演, etc. If you spell in Hiragana, we sometime do not understand which word you mean.