While I agree with you that it shouldn't be about the "freshest" both Asylum and Portal 1 were by far the better games.
I won't argue about portal since I don't really care about them but there's no way that Asylum is better. City greatly expanded on all of the gameplay stuff while some of the non important stuff like pacing and story may have suffered a bit in places. It's the ultimate superhero game of the generation (provided Origins doesn't blow it away). Go back and play AA after playing AC, it's really tough to put up with all of the downgrades in combat, bosses and the riddler stuff.