In my experience, Katakana is like print for the Roman alphabet, Hiragana is like cursive and Kanji is like a cross between caligraphy and sanscript (nice to look at but not many bother to learn it today). I would definitely start with Katakana first. It is the basic alphabet used for Japanese media today. Most of the characters consist of basically 3 pen strokes.

*Protip* Pay special attention to the direction of the strokes. Passing the stroke the wrong way can make the letter look like a different one (thus making you say something completely different). I know from experience.

Hiragana would be second. It will me much easier since it is very close to Katakana and only has an average of 4 strokes. This alphabet is generally used for handwriting.
Hope this was of some help in your decision.