Very this about Curse, which is my favourite. It really is about that atmosphere which makes each space feel unique, special, and interesting. Even when you have so many different locations within a single island, like Plunder with its beach, town, swamp, jungle, grassy knoll, etc; they somehow all seem to hold together to form a cohesive whole. And I've always loved Blood Island, it's just completely magical to me.
But beyond that, i think this is the one that hits my sense of humour the most. I think it's got the best lines, visual gags and references.
Then again, I played Curse a lot when it came out. I mean, a lot. You know how sometimes you'll put on music or a TV show for background noise while doing something else? It got to a point that I would do that with Curse. Forget speedruns, I'd go as slow as possible - selecting every longer bit of dialogue, and making sure to extend the conversation trees as much as possible. I would sometimes just leave it sitting on a single screen for a bit while doing something else IRL, waiting to run through all of the different Guybrush asides that could happen, or to hear the whole of Slappy Cromwell's performance rehearsal. I still can quote the game in its entirety from memory. So it may be that it's just the sheer amount of time I spent in it that has made Curse my favourite.
When EMI came out, I was so excited and I wanted to like it so badly. I tried to convince myself I was enjoying it. When I finished the game, I cried actual tears because I was so disappointed in it. I've only played it through three times, and one of those was last year. I'd seen an article (can't find it now) that was toting EMI's merits and saying that it basically got a bad wrap because of the fanbase's love for the earlier games and their aversion to change. So I decided to give it another shot - I thought that surely now, with some distance and age, I'd be able to see the good in it. That I could, in some way, divorce it from the franchise and see it objectively as a unique adventure game. That was not the case. I still hated it. I just found it tedious, not funny, and shallow as an overall experience - even before the Monkey Kombat.
MI2 is runner-up for me, great storyline, good characters (esp. Largo, Kate, and Gov. Phatt), but it falls apart for me on Dinky and I've actually replayed it multiple times and just stopped when I get there because I don't want to bother with Dinky. I've had similar experiences with MI1, where once i'm on Monkey Island, I just don't want to go through the island bit.
Tales is a hit-and-miss for me, and it really goes episode for episode, which makes it hard to rank but I was glad for it overall.