Cape Riverne before the level cap was removed was probably the worst. True-sight hippogriffs, having to farm scales from mobs above your level, twisty map. And (from post-cap experience) it seems to be implemented in such a way that party members in different parts of the zone won't even show up on map markers. It used to take like two hours to get to a mission fight BCNM because people are stupid and somebody was always getting aggro and/or lost trying to follow invisible people.
Then there are those split ToAU zones where you have to remember exactly which teleporters to take from Nyzul, or which tunnels from Wajoam/Blafhau to get to each sub-map.
Yorcia Weald is the new most annoying zone. The map gives you no clue where you can and can't go, true-sight panopts, and the timed shrubbery gates (only open during certain game day hours) that SE apparently got rid of after a few updates because they were such a pain in the ***.
Also, some CoP zones have really bad maps, and you had to go through non-soloable stuff to get them back in the day. Promy maps are just fuzzy stains, Aqueducts don't have half the zone marked, Sacrarium maze is just six squares, and I think the Riverne map still doesn't have overlay markers where the displacements are. For all of those I just use the wiki maps on my laptop.
I was running my alt character with my girlfriend through Jugner (S) to get to Sandy (S) for our first time there. I hadn't done that run since WoTG came out. I raged so hard at that map it got me wondering what everyone elses most hated zone was.
The right way to do that is to first unlock Windurst (Bastok works too, if you like the smell of smog), join the Cobras, then do a campaign op or two for allied notes. Then you can zone into Jugner (S) from Batallia, retrace back home, and simply warp to the outpost. Otherwise you basically have to go all the way through Vunkerl (S) to get anywhere in Jugner. Vunkerl is a pretty bad zone to have to run through to get back to south Jugner, but it's still not the ***-you-maze of one-way drops that Jugner is.
EDIT: Oh yeah, and trying to get to just the right cave at the top of Ulegerand Range by sliding down the cliff. And that one glacier thingy that only opens during clear weather. At least that one has a warp point behind it now. It also lets you reach one of the coolest areas in the game, an outside view in the BCNM area.