You can't apply criteria to favoritism.
If you could, it wouldn't be.
Well, that's not exactly true. You can't apply one specific criteria to multiple people, but each individual can use their own criteria to choose their favorites if that is how they pick.
Anyways, the criteria isn't for favorites, it's for picking which strips should be listed on the "Best Comics" page on the wiki so that we don't just get a page that lists every comic (which would be the inevitable result if we just listed everyone's favorites). Perhaps the easiest requirement would be strips that a number of people agree as being their favorite/the "best" (as opposed to ones just anyone picks as their favorite).
I don't know, making a "Best Of" list is kind of futile as most of the time not everyone is going to agree no matter what criteria you use. It really should be a "Pretty Decent Selection Of" instead lol.
To get back on topic, my favorite I think is 564, where Dora kisses Marten on the rooftop.