Zone explore order

[Laerte]

Alt Korpul is full of bandits and has fewer undeads.

[Charlie_B]

Zone order takes alt/non alt into consideration as well.

In rough order of difficulty, from easiest to hardest (and this is certainly up for debate, and not necessarily entirely spoiler free, though it stops at dreadfell)

Norgos Lair
Trollmire/Alt Trollmire (no real difference there, but you're skipping Bill either way)
Alt Korpul
Alt Norgos Lair
Korpul
Alt Heart of the Gloom
Heart of the Gloom
Thieve's Tunnels (Merchant dungeon. Do whenever it shows up, really)
Crystal Caves/Alt Crystal Caves (no real difference there)
Rhaloren camp
Alt Rhaloren camp
Bill (Can be done earlier, but I'm cautious here.)
Old Forest
Maze
Alt Sandworm Lair
Alt Old Forest (Might be outdated. I feared this place when it was new, but the boss got toned down a lot. My fear stays though.)
Sandworm Lair (Not so much threat, as royal bloody nuisance. More loot, but more annoyance, timewasting, irritations)
Daikara
Tempest Peak
Temporal Rift (Can do just after diakara, if confident. Build varies this.)
Hidden Compound (slavers dungeon. Lower threat if you're just killing the slaves.)
Alt Maze
Ruined Dungeon (Can be easier, but randomness of gaurdians can make it a much bigger threat, if not well prepared)
Alt Daikara
Halfling Ruins
Dreadfell
Mark of the spellblaze (Can be done just pre-dreadfell, but there's not much reason to, unless you have special plans, and the risk is significant.)

Fairly concise ranking on difficulty. Note that while a few are more or less interchangeable, and others might be adjusted based off class/build (alt maze is MUCH worse for pyromages or anything that's hurt by silence/is frail), this is a rough estimation of difficulty, as viewed for a player on normal/adventure. I'm sure someone will debate this, especially for higher difficulties, but it's my take on it.

Golem graveyard can be tossed in, but there's practically no value in doing so. Minimal enemies, tiny area, no real loot. Unless you're on the absolute edge of a levelup you want, there's no point in doing it at all.

I'd say this is a pretty good list, although I'm a bit less cautious about Bill who I've never had a problem killing (I play on Nightmare). In particular I agre with Mark of the Spellblaze - other guides put this much earlier in the list when it's by far my most feared/hated zone thanks to that damn Corrupter.

I'm not sure about the Old Forest, if you're carrying on underwater. Personally I find that the hardest t2 zone.