Mr. Lisa Goes To Washington...No, wait, that's not in the poll. I think it's ok that's not included cause then you'd have to include every episode that includes some sort of trip, like going to Canada in The Bart Wants What It Wants.
The episodes included in the post are easier to compare cause they are all non-USA related trips, and they all have thin plots and rely on stereotypes...and that's why I'm not a fan of them. They just seem to have easier satire than the rest of the series and in the new seasons they have became a formula for the weaker episodes, done with almost zero effort.
But at some point I was actually a big fan of Bart Vs Australia, and I even considered it my favourite episode. I just loved the gags in it and the family interactions, especially Bart being oblivious about the hemispheres and Homer jumping from one country to another, or the "scary" ending with the koala. I still love these bits and the first act which showed me the existance of the Coriolis effect, but something about the episode as a whole feels worse now. I don't know if it's the episode's flaw or it's the influence of the subsequent vacation episodes, but it looks less special and the plot seems thinner now.
It's still one of the best but there are a couple of subsequent ones that are almost as funny and do a nice job assembling the gags and those are Thirty Minutes Over Tokyo and Blame It On Lisa. So it's kind of a tie between those three.
Everything else is pretty flawed. I do like a number of gags in Simpson Safari, but the bad ones are truly awful, still it's not such a bad vacation episode after watching some of the new ones, but still a C- or something like that.
Kiss Kiss Bang Bangalore is kinda saved by the subplot but it's a bland collection of gags that only sometimes gets fun because of its absurdity. A lot of wasted potential for satire about outsourcing. C+
Goo Goo Gai Pan is also full of wasted potential. What could have been an hilarious and emotional episode about Homer pretending to be Selma's husband and Selma adopting a baby turns into a lousy Homer in pain gagfest full of chinese cliches. Not as awful as I thought at first watching but still very flawed. C-
The Regina Monologues has some fun moments before the incident with the Queen (the Trainspotting scene is pretty cute) but once that excuse for a plot begins it turns completely awful. D
In The Name Of The Grandfather has what it looks like a decent plot but it's terribly underdeveloped and the gags are dull and don't feel very simpsonic. C/C-
The Greatest Story Ever D'ohed is the worst one, again a promising plot about Flanders and Homer's beliefs and a potential satire about religion turns into a paper-thin plot with endless dialogues of the unfunny Sacha Baron Cohen character and wacky Homer's antics that are not very funny either. F, mainly because of S.B.C., maybe I'll give it a better grade on rewatching but it was really one of those episodes I had to do an effort to watch it on the whole even once.
I'm going with Blame It On Lisa, maybe just because Bart Vs Australia looks like the obvious choice.