which Nietzsche is best?

90 Minute Nietzche, is a favorite of Americanns

I looked it up, and it's not solely Nietzsche's writings. It's some other guy's interpretation. Im required to read a book he authored, and give my interpretation, I think.

I've read both Behold The Man and Thus Spoke Zarathustra, neither are that long or particularly complicated.

With that attitude you won't go far... Had it been my case and I would be asking for the opposite criteria...long and complex are supposed to be appealing.

how is long and complex supposed to be appealing? some things long and complex are long and complex for the sake of being long and complex when they could've expressed the same idea to the same extent in ten times fewer the words.

...well that's true when its true isn't it ?
There is a distinction between complex and complicated, and I for one, would not recommend any complicated reading.
(specially in Philosophy where being clear is absolutely necessary)
Not to confuse with being dumbed down or simplified.

I understand.
according to your criteria then, do you have a recommendation?

Not in this case no. I don't have a particular preference when it comes to Nietzsche. Not only his writing is awfully misleading but his ideas on the roll of Man in the world are wrong at a base level. Nietzsche is somewhat trivial and lacks depth on his departure of metaphysics...hence its appealing to young men, naive scientists, and American pragmatic philosophy at large.
Believing man is free to build its destiny against Being is an appalling act of wishful thinking.

he might be important to study in terms of influence though

Twilight of the Idols is one of his shorter works, and yet a pretty good summary of his later, more influential φ.

thank you

In that sense he was very important in the context of the first half of the XX Century and still is today. Twilight of the Idols is not a bad choice.

I find Nietzsche peatzsche.