I know there are all sorts of variables to be taken into consideration (e.g. the quality of individual components a bike comes with off the rack), but, generally, across the board, where is the best money spent to improve components when buying an entry-to-mid level bike? I'm thinking breaks...

Hello bike friends!!! I am building my own "soft all mountain" hardtail (yes, hardtail I hope it works) And I am using mainly Sram X7 to X9 stuff :) Right now, I'm the process of buying some disc brakes and they will be my first disc brakes ever, so I was wondering if someone could advice me...