algorithm - QuickSort - Pivot Selection , Random Element Vs. Random Index -

i have array of size n contains number 1 10 ( floating point numbers included). strategy better pick pivot quicksort:

1. picking random element between 1 , 10.
2. picking random index between 1 , n.

i believe 2nd strategy better because of lower probability of picking element in less 10% or greater 10% of array. maths behind 1st strategy? worst case of sorted array worse 1st strategy or 2nd?