Underground Passage and Temple of Ikov are both on my hate-list, but in general I think the osrs quests are doable and fun. The only part about questing I hate is when I forget to bring a necessary item and have to spend another 5 minutes getting it, which is an issue common to most longer quests.
I love questing. Except for underground passage.. That quest is straight AIDS and whoever created it is evil. On the other side of the spectrum, my favorite quest is Monkey Madness .
I believe underground pass can take anywhere from 1-4 hours to complete. Obviously closer to 4 was when I first did it, I had low agility, and no energy potions to speed things up. Even though it can be completed way faster with high enough skills and energy potions, it's left a bad taste in my mouth ever since.
For me it's Ratcatchers. Just a really frustrating quest overall with buggy design.
I actually found Underground Pass to be one of the more enjoyable quests in the game. I think that it's very well-made and pretty immersive, as far as quests go. As long as you have a decently high agility level and bring summer pies/stamina pots, it shouldn't really take longer than 30 minutes, from my experience.
When building new accounts, I hate RFD. Requirements is sooo many quests and skills.
Temple of Ikov blows too. Not a fan of agility, so falling down to the bottom is gay.