of course there r differences between hiragana, katakana(except for "he" char),  well i started from hiragana 1st bcoz i think i can see many hiragana words like in japanese tv shows(although there r also kanji) or in some beginner japanese lessons, and there are also kanji words that come with furigana(izzit?... the small word they put on top of kanji to help wit the pronunciation, correct me k!), which usually hiragana(maybe bcoz the origin of the word, which is japanese word)..... but thats depends... some say hiragana more difficult to memorize same say katakana (for me katakana is more difficult  ),  try to make a table for those words, .... i cant tell more bout kanji coz i myself hv hard time memorizing them  ... all this is base on my experience and thought  , sorry if it didnt help a lot 

interested in the language and be able to read, write, in japanese, you must know all 3 kana.... you can learn/memorize all 3 at once if u want, or u can concentrate on 1 kana 1st(for katakana n hiragana)....

but for me, its better to know hiragana 1st becoz, along the way u might also learn bout the grammar, the particles,which is written in hiragana(although many japanese beginner lessons comes in romanji),.... ... n many japanese words are written with the combination of kanji and hiragana...