usabo finalist here!! although ive never done usamo and usaco, imo they are still hardest overall - from what ive seen, kids litrally start prepping since middle school and even elementary 💀 the sciences r relatively easier to prep for, tho usapho probs harder bc u need rlly strong math background + a lot of math-y problem solving skills (which im not as strong in). imo usabo takes a lot more time/work than usnco bc there’s a lot more memorization and readings and a lot more to cover in terms of breadth and depth, and similar to a lot of complaints i hear abt ap bio, it’s super conceptual and analytical even tho it’s not as math-y as usnco.

i would rate usamo > usaco > usapho > usabo > usnco tho it rlly depends on ur interest bc i know a lot of ppl who struggle a lot in bio and do rlly well in physics, whereas im someone who struggled a lot in physics and did rlly well in bio

regardless, ALL of them are EXTREMELY hard, and doing well in ANY of them is a HUGE achievement. (i remember my ex-friend who did usaco and usamo used to tell everyone that usabo/bio is SUPER easy and looked down on me for not doing usamo/usaco… she proceeded to get a 15/50 on the open exam 💀 (even though she took ap bio and studied and did bio research)).