Something of a language-evolution-now observation: I had always thought that "an historical" is wrong, and the result of us getting lazy with our aspirated "h" sounds. It should be printed as "a historical," at least for now. Nonetheless, I and many others pronounce it "anistorical" when speaking quickly, so I'm totally down with not pronouncing things completely correctly.
I do cringe when people pronounce the phrase "an historical" very carefully in their public speaking voices. Kinda like the CEO of a company carefully pronouncing "LOL" without irony. Course, this is how language changes over time, so what we're witnessing is really the same sort of thing that took the aspiration OUT of "who" and "what". Or changed all the "in-" prefixes to "im-" in words beginning with bilabials, like "impossible" or "immoral".
But there's more to the story than that, involving several opinions. Tina Blue has more, invoking a whole hierarchy of syllabic stress:
In the word historical, the first syllable is actually slightly stressed, though far less so than the second syllable, which carries the primary stress. But in the word hotel, the first syllable, though less stressed than the second, is significantly more stressed than the first syllable in historical. In historical, the first syllable receives only tertiary (third-level) stress, whereas in hotel, the first syllable receives a secondary stress so strong that it is nearly equal to the primary stress on the second syllable. For this reason, the h in a hotel is pronounced almost as fully as the h in a hot day.