Act 2, Quest 2 (the Horadric Staff).
I hate underground tunnels, and the maggot lair is one of the worst. You go down with a big group, and 1 person stands in front killing things, with everybody else backed up behind him preventing him from retreating if he's about to die. At least the Viper Amulet can be somewhat useful for new characters.
The single best quest is Act 3, Quest 2 (Khalim's Will). Izzy is a close second, but in the end I'd rather have fewer skill points on my final characters than be left without the single greatest tweaking item in the game. Every single character I make uses Khalim's Will at least through Act 1, and it's hard to beat 1-hit kills for practically an entire act. Yes, these tunnels are horrible, too, but at least the monsters are a little more entertaining than in Act 2. I always love those bats that guard the entrance to the Sewers 2. Plus, you have to click on that little wheel-thingy to make the stairs open. Best of all, you only have to do the quest once, and then you can reuse the item for every single character you make. Much better than having to wander around in hell, muttering under your breath about how cheap gloams are, and then whacking on a big stupid monster that does no damage but has horrifically high HP combined with freezing attacks that make you hit slower. What a crap combination that is.
And personalization sucks? Constantly worrying about resale value of something is a horrible way to play the game (or deal with anything in life, for that matter). Yeah, my couch is a cheap POS, but it's the most comfortable couch I've ever had, and that's what matters, not if I could get $15 more at a rummage sale if I have to eventually sell it. If I find some godly rare, I'm definitely sticking my name on it. Who doesn't remember X-Factor Celine's mage plate? I bet you wouldn't if it was just some random item name. It's just too bad you can't personalize every single item on a character. Well, you kind of can; just make a few characters with the same name except for periods at the end of the names or something like that, rush them, and personalize your entire outfit. Now that's classy.