It depends on what your weakness is. If you're better at just general positional play, then get the endgame course. If you feel confident in your endgame knowledge and are weak at positional play, then get the "reassess your chess." Based on your rapid rating, I'd probably recommend reassess your chess as that is more immediately critical, but if you have the time and money to get both and really want to improve get both.
which is the best book silmans complete endgame course or how reassess your chess

tell me which is your choice