I need to book a ticket for the middle of November from Buenos Aires to Denver. The prices are pretty high, but is it better if I wait a while and the prices will hopefully go down or would it be better if I go ahead and book the flight since it is less than 90 days away from now? I have miles with both Oneworld and soon Star Alliance since Avianca is joining Star Alliance.
My other question is would it be better (do they offer deals in the offices that are not offered online?) to book the tickets online through the airline websites or should I go into the office of the airline? I have both an Avianca and American Airlines office close to where I live.
Sorry if I posted this in the wrong forum, but I couldn't figure out where this question would belong

You don't have "oneworld miles" because there is no such thing.

Austinrunner, I meant to say I have miles with a Oneworld airline, but really, I never said I had "Oneworld miles." The exact quote was "I have miles with both Oneworld and Star Alliance." I guess I should have clarified that, but I don't think the question is difficult to understand.

As above no such thing "as miles with Oneworld".
You need to go the airline web site. Each airline freq flyer program is different. There is no guarantee a reward seat will be available with your program.

Which airline? The rules of every airline are different.

Sorry for the confusion,
The Oneworld airline that I have miles with is American Airlines. I will not be using my miles to buy the ticket. I would just prefer to fly on an airline that is either with Oneworld or Star Alliance so the miles could transfer easier (At least I thought they might transfer easier within the same alliances).
To simplify my question would it be better to book online directly through the Avianca or American Airlines website or would it be better to go to the office of the airline (Would they have deals in the office that are not available online)? Since there are fewer than 90 days left until the flight leaves would I be more likely to get a better price if I go ahead and book now or is the price likely to go down if I wait? I know it's kind of a guessing game, but in general, what is the window of time before the flight with the lowest prices for international flights? I have been watching for at least 20 days and the prices haven't really changed.

Unfortunately, practically, miles transfer between airlines is impossible even same alliance meners.

AA forum is better place to ask.

Yes, perhaps technically it is difficult to transfer miles between One World members.
However, there is no need to transfer miles. Merely give the AAdvantage number at booking and ask that the miles be credited initially to your AAdvantage account.
Note that this only works within the One World alliance or with AA partner airlines.

Rens

You may find that paying a human for a ticket incurs a booking fee whereas paying your computer for the ticket avoids the booking fee. It is rare (IME) for cheaper prices in airline offices. Web sites such as expedia may have cheaper prices, but let the buyer beware. Personally, I'd book now so I get a seat on the day I want to travel rather than wait in hope for a change that may not happen - indeed may push you into a higher fare category because someone else got in first.