[SakanaMidori]

Probably katakana...

But you'll definately need all of them.

Kanji is definately the hardest, so you should start learning those first, continue learning that as you learn katakana, keep learning kanji, and learn hiragana.

That's probably the most affective way to learn it.

I actually learned hiragan first, then katakana, and kanji(which I am WAYY behind in)