Amherst college or Washington University St. Louis

Should I apply to Amherst college early decision or University of Washington St. Louis early decision?
I am international student, interested in applying for computer science Undergraduate and need financial assistance from colleges. Where do you think I have more chance as an international student with financial need?

Amherst.

International students seeking fin aid should consider all US colleges reaches. With that said, I recommend Amherst given the choice in your OP. Amherst is need blind for internationals, WashU need aware. Both meet full need, as defined by them.

Look at the CDSs to get a sense of their relative numbers:

Total undergrad population at WashU - 7,356 degree seeking, 551 internationals of which 66 received fin aid (average $48K). That’s around 16 international students per year who receive fin aid. B2 and H6 https://wustl.edu/wp-content/uploads/2019/06/wustl-cds-2018-2019.pdf

Amherst total undergrad population - 1,855. 151 internationals of which 135 received fin aid (average $66K).
https://www.amherst.edu/amherst-story/facts/common_data_sets/2018 B2 and H6

You can do similar analyses for other schools, using their CDSs. You may not find a more generous school than Amherst for internationals, but obviously very difficult to gain acceptance. Good luck.

Both are extremely tough admits( especially Amherst)for anyone, let alone an international needing financial aid. I would guess that the CS course offerings at WashU would be more extensive.

Both are outstanding schools, but neither would be my 1st choice for CS.

Amherst (especially based on @Mwfan1921 's post)