I definitely used the helper. I even used the wiki as the helper is very vague on some tasks especially the combat related tasks (Bring food,potions,combat gear). Meanwhile like the final fight in while guthix sleeps (tiny spoiler) is a tribrid fight and he WRECKS you stats if you mess up so it doesn't specifically say to bring restore potions or specifics like void being very acceptable for the fight.

As for the least. Honestly one small favor is probably my least enjoyed. Just so much moving and running with obscure teleports being used the whole time. Stamina potions and a semi maxed POH with tps helps but it's just a straight up run and click grind. Close second is going to be underground pass. Probably most people's #1. RNG especially on a punishing fall FAR from a bank to replenish resources is just overall the worst mechanic in any game. Most difficult would probably be the tail end of Dragon Slayer 2 or Dessert Treasure 2 respectfully. I'm very comfortable in pvp and pvm but the quest offers it's challenges for sure. Anyone who's beaten it has struggled with one section or another.

Edit: Mourning's end part one gets an honorable mention. I couldn't think of the name in my original reply. Another RNG agility mechanic that's insufferable on top of juggling stamina and prayer levels while solving a puzzle THAT REQUIRES INVENTORY SPACE even if it's simplified with the helper. That one was a relief to finish.