Factions is top for me too, I love the scenery there. In the past I've vanquished areas there then gone wandering around the whole explorable to look for things I never noticed before. I really enjoy the aesthetics of the Jade Sea and even though the city can be a little ugly it hides some interesting things such as the empty moving rocking chair outside KC and the many cats in different places. Also the mouse that comes out of the hole in tahkani temple is cute (iirc that's the right spot).
Second would be Prophecies just because it has some areas I don't like. I'm also not a fan of the sand (ugh, desert). My favorite spot in prophecies would have to be kryta with it's lush greens and beautiful sky. My favorite spot to afk used to be in Gates of Kryta sitting on the hill with my froggy friend.
Last would have to be NF, again, did I mention I hate sand? The only area in NF I consistantly play is the island of istan, and I only play there because I like the no req insc 8ar shields that can drop there.
EotN isn't a campaign but it probably fits on my list about even with Proph. I like most areas, I enjoy some dungeons and it's mostly aesthetically pleasing to me. The probable worst thing for me about EotN is the asurans, I dislike their smug atittudes and bunny-looking faces and would love to smack Vekk around a bit.
...which leads to favorite tonic combo of Vekk tonic + lunatic court helm (flaming pumpkin head) = Vekk on fire.