We will be part of the Berlin-Prague-Vienna tour in June. We have a 6 am flight out of Vienna. Our hotel is the Hotel Mercure Josefshof Vienna. What is the best way to get to the airport and how long should we allow for the trip.
You have at least three choices: subway, taxi, bus. In September, 2010, I stayed at the Hilton on Schottenring. Although my flight was a few hours later than yours, I took a taxi, because I didn't wish to get up in the middle of night to walk to the u-bahn station, take the u-bahn to where I'd catch the faster s-bahn (which makes just two trips per hour), and then walk to the airport. The taxi cost me E40 plus tip. For subway, you can take u-bahn to s-bahn to airport, or CAT (city air transport). S-bahn is faster than u-bahn and is cheaper than the dedicated airport to city CAT subway. I can not help you on bus transport. best wishes.
Where does you flight out of Vienna take you? If it stays in Europe, you do not need to be at the airport 2 hours early because none of the counters should be open. If you are flying directly to the US, which I doubt, all bets are off as to how early you have to be at the airport. We had an early morning flight out of Vienna last summer (2011) and ended up at the airport before any of the counters were open so we had to sit around and waste time. We scheduled a taxi thru the place we were staying in, but to advancing age, I am unable to remember how long it took. You might want to contact the last place you are staying (either e-mail or phone call remembering the time difference between the west coast and Europe) to see if they have any suggestions and costs. We have taken our last very early flight when headed home from Europe where we go every summer. Starting this next summer we will be flying into our airport that flies to Seattle
the night before our flight and staying at a nearby inexpensive hotel.