AD9515 Clock Input general questions

Hello,

I have to use the clock distributor AD9515 in my design to generate a 250MHz clock, and since it's pretty new to me, I'm not sure what clock input I should use ? 
A simple quartz, another clk generator IC that I will put upstream ... ?

And also, what is the differences between using a 1GHz quartz with a x4 divider or a 250MHz quartz with x1 div ?

Thanks 

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